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1: Kw of pure water is 10⁻¹² at 60°C. The pH of pure water at 60°C is:
a) 6
b) 12
c) 7
d) 8
✅ Correct Answer: (a) 6
🔎📌 Short Reason
Kw = [H⁺][OH⁻] = 10⁻¹² ⇒ [H⁺] = 10⁻⁶ ⇒ pH = 6.
🔎🧠 Step by Step Reasoning
Kw = [H⁺][OH⁻] = 10⁻¹²
[H⁺] = [OH⁻]= [H⁺]² = 10⁻¹² ⇒ [H⁺] = 10⁻⁶ M
pH = −log[H⁺] = −log10⁻⁶ = 6
.
🔎📌 Short Reason
Kw = [H⁺][OH⁻] = 10⁻¹² ⇒ [H⁺] = 10⁻⁶ ⇒ pH = 6.
🔎🧠 Step by Step Reasoning
Kw = [H⁺][OH⁻] = 10⁻¹²
[H⁺] = [OH⁻]= [H⁺]² = 10⁻¹² ⇒ [H⁺] = 10⁻⁶ M
pH = −log[H⁺] = −log10⁻⁶ = 6
.
2: H₂SO₄ is stronger acid than CH₃COOH because:
a) It gives two H⁺ ion per molecule
b) Its boiling point is high
c) Its degree of ionization is high
d) It is highly corrosive
✅ Correct Answer: (c) Its degree of ionization is high
🔎📌 Short Reason
The strength of acid is measured by its degree of ionization and Kₐ or pKₐ values. High degree of ionization and high value of Kₐ (greater than 1) or low pKₐ values indicates strong acid and vice-versa..
🔎📌 Short Reason
The strength of acid is measured by its degree of ionization and Kₐ or pKₐ values. High degree of ionization and high value of Kₐ (greater than 1) or low pKₐ values indicates strong acid and vice-versa..
3: Rate constant of a reaction is affected by:
a) Conc. of reactants
b) Conc. of products
c) Temperature
d) Reaction time
✅ Correct Answer: (c) Temperature
🔎📌 Short Reason
Rate constant of a reaction is affected by temperature only. The rate constant depends only on temperature because it reflects the fraction of molecules with enough energy to overcome the activation barrier. Concentrations and time affect the rate, but not the constant itself.
🔎📌 Short Reason
Rate constant of a reaction is affected by temperature only. The rate constant depends only on temperature because it reflects the fraction of molecules with enough energy to overcome the activation barrier. Concentrations and time affect the rate, but not the constant itself.
4: The purpose of using of catalyst in a chemical reaction is to change:
a) Equilibrium constant
b) Enthalpy of reaction
c) Nature of reaction
d) Activation energy
✅ Correct Answer: (d) Activation energy
🔎📌 Short Reason
The role of a catalyst is to change the activation energy of the reaction. However, catalyst does not change Gibbs energy of reaction, enthalpy of reaction and equilibrium constant..
🔎🧠 Step by Step Reasoning
📌Equilibrium constant (K) is not changed by a catalyst. It only affects the speed at which equilibrium is reached, not the position of equilibrium.
📌Enthalpy of reaction (ΔH) is a thermodynamic property and remains unchanged.
📌Nature of reaction (the overall chemical transformation) is not altered
.
🔎📌 Short Reason
The role of a catalyst is to change the activation energy of the reaction. However, catalyst does not change Gibbs energy of reaction, enthalpy of reaction and equilibrium constant..
🔎🧠 Step by Step Reasoning
📌Equilibrium constant (K) is not changed by a catalyst. It only affects the speed at which equilibrium is reached, not the position of equilibrium.
📌Enthalpy of reaction (ΔH) is a thermodynamic property and remains unchanged.
📌Nature of reaction (the overall chemical transformation) is not altered
.
5: Ionic reactions are classified into
a) Slow reaction
b) Fast reactions
c) Reversible reaction
d) Moderate reactions
✅ Correct Answer: (b) Fast reactions
🔎📌 Short Reason
The reaction between ions is very fast. Hence ionic reactions are fast reaction.
🔎🧠 Step by Step Reasoning
📌 Ionic reactions occur in aqueous solutions where ions are already present and free to move.
📌 When oppositely charged ions come close, they combine almost instantly because there is no need to break strong covalent bonds.
📌 The reaction rate is therefore very high — practically instantaneous — compared to covalent reactions
🔎📌 Short Reason
The reaction between ions is very fast. Hence ionic reactions are fast reaction.
🔎🧠 Step by Step Reasoning
📌 Ionic reactions occur in aqueous solutions where ions are already present and free to move.
📌 When oppositely charged ions come close, they combine almost instantly because there is no need to break strong covalent bonds.
📌 The reaction rate is therefore very high — practically instantaneous — compared to covalent reactions
6: The best alternative term for the velocity of reaction is:
a) Rate of appearance
b) Rate of disappearance
c) Average rate
d) Instantaneous rate
✅ Correct Answer: (d) Instantaneous rate
🔎📌 Short Reason>
Velocity of reaction is also termed as Instantaneous rate.
🔎🧠 Step by Step Reasoning
📌 In chemical kinetics, the term velocity of reaction is an older synonym for rate of reaction. 📌 The rate of reaction can be expressed in two ways:
📌 Average rate → change in concentration over a finite time interval.
📌 Instantaneous rate → change in concentration at a particular instant (the slope of the tangent to the concentration vs. time curve).
📌 Since “velocity” implies the exact speed at a given moment, the best modern equivalent is the instantaneous rate.
📌 Rate of appearance/disappearance are specific to products or reactants, not the overall velocity term.
🔎📌 Short Reason>
Velocity of reaction is also termed as Instantaneous rate.
🔎🧠 Step by Step Reasoning
📌 In chemical kinetics, the term velocity of reaction is an older synonym for rate of reaction. 📌 The rate of reaction can be expressed in two ways:
📌 Average rate → change in concentration over a finite time interval.
📌 Instantaneous rate → change in concentration at a particular instant (the slope of the tangent to the concentration vs. time curve).
📌 Since “velocity” implies the exact speed at a given moment, the best modern equivalent is the instantaneous rate.
📌 Rate of appearance/disappearance are specific to products or reactants, not the overall velocity term.
7: Order of reaction is the power to which concentration of reactant is:
a) Lowered
b) Raised
c) Stopped In the reaction
d) Constant
✅ Correct Answer: (b) Raised
🔎📌 Short Reason
Order of reaction is the power to which concentration of reactant is raised. For a general reaction; mA + nB → P, order is written as .
🔎🧠 Step by Step Reasoning
Rate = K[A]ᵐ [B]ⁿ; Order of reaction = m + n
.
🔎📌 Short Reason
Order of reaction is the power to which concentration of reactant is raised. For a general reaction; mA + nB → P, order is written as .
🔎🧠 Step by Step Reasoning
Rate = K[A]ᵐ [B]ⁿ; Order of reaction = m + n
.
8: In the reaction A→B, the rate of disappearance is written as:
a) dᴀ/dₜ
b) −dᴀ/dₜ
c) dв/dₜ
d) −dв/dₜ
✅ Correct Answer: (b) −dᴀ/dₜ
🔎📌 Short Reason
The rate of disappearance of reactant is shown by a negative sign. From reaction stoichiometry, one mole A gives one mole of B. Rate of disappearance of reactant A = −dₓ/dₜ = −dᴀ/ dₜ
🔎🧠 Step by Step Reasoning
In chemical kinetics, the rate of disappearance of a reactant is always written with a negative sign. This is because the concentration of reactant decreases with time.
Mathematically: Rate of disappearance of A = −d[A]/dₜ
The negative sign ensures that the rate is expressed as a positive quantity, even though [A] is decreasing.
For the reaction A → B:
Disappearance of A → −dᴀ/dₜ
Appearance of B → +dв/dₜ
🔎📌 Short Reason
The rate of disappearance of reactant is shown by a negative sign. From reaction stoichiometry, one mole A gives one mole of B. Rate of disappearance of reactant A = −dₓ/dₜ = −dᴀ/ dₜ
🔎🧠 Step by Step Reasoning
In chemical kinetics, the rate of disappearance of a reactant is always written with a negative sign. This is because the concentration of reactant decreases with time.
Mathematically: Rate of disappearance of A = −d[A]/dₜ
The negative sign ensures that the rate is expressed as a positive quantity, even though [A] is decreasing.
For the reaction A → B:
Disappearance of A → −dᴀ/dₜ
Appearance of B → +dв/dₜ
9: Only one pair of liquid in the following set does not obey Raoult’s law, identify it:
a) Methanol and Ethanol
b) Benzene and toluene
c) n-Hexane and n-heptane
d) Ethanol and Acetone
✅ Correct Answer: (d) Ethanol and Acetone
🔎📌 Short Reason
When acetone and ethanol are mixed, the weakening of hydrogen bonds in ethanol takes place. Hence, an ideal solution is not formed. This leads to deviation from Raoult’s law (negative deviation)..
🔎📌 Short Reason
When acetone and ethanol are mixed, the weakening of hydrogen bonds in ethanol takes place. Hence, an ideal solution is not formed. This leads to deviation from Raoult’s law (negative deviation)..
10: Identify the incorrect statement about colloidal solution:
a) It shows Tyndall effect
b) Its particles movement is Brownian type
c) Its particle size is less than 1 nm
d) Its physical appearance is translucent.
✅ Correct Answer: (c) Its particle size is less than 1 nm
🔎📌 Short Reason
In colloidal solution, the particles is in between 1 nm to 1000 nm 6.
🔎📌 Short Reason
In colloidal solution, the particles is in between 1 nm to 1000 nm 6.
11: Which is not a colligative property?
a) Lowering in vapours pressure
b) Elevation in boiling point
c) Depression in freezing point
d) Atmospheric pressure
✅ Correct Answer: (d) Atmospheric pressure
🔎📌 Short Reason
Atmospheric pressure is an external physical condition, not related to the number of solute particles in a solution. Therefore, it is not a colligative property.
🔎🧠 Step by Step Reasoning
Colligative properties depend only on the number of solute particles in a solution, not on their identity.
The four classical colligative properties are:
⚡Relative lowering of vapour pressure
⚡Elevation of boiling point
⚡Depression of freezing point
⚡Osmotic pressure
🔎📌 Short Reason
Atmospheric pressure is an external physical condition, not related to the number of solute particles in a solution. Therefore, it is not a colligative property.
🔎🧠 Step by Step Reasoning
Colligative properties depend only on the number of solute particles in a solution, not on their identity.
The four classical colligative properties are:
⚡Relative lowering of vapour pressure
⚡Elevation of boiling point
⚡Depression of freezing point
⚡Osmotic pressure
12: Effect of pressure change play significant role in the solubility of:
a) Solid into liquid
b) Liquid into liquid
c) Gas into liquid
d) All of them
✅ Correct Answer: (c) Gas into liquid
🔎📌 Short Reason
The solubility of gas into liquid is significantly changed by the change in pressure obeying Henry’s law accordingly the solubility of gas in liquid solvent is directly proportional to the pressure.
🔎📌 Short Reason
The solubility of gas into liquid is significantly changed by the change in pressure obeying Henry’s law accordingly the solubility of gas in liquid solvent is directly proportional to the pressure.
13: According to Raoult’s law the relative lowering of vapour pressure is equal to:
a) Molality
b) Mole fraction of solute
c) Mole fraction of solvent
d) Molarity
✅ Correct Answer: (b) Mole fraction of solute
🔎📌 Short Reason
According to the third form of Raoult’s law, the relative lowering of vapour pressure is equal to the mole fraction of solute.
∆P/Pₒ = X₂ ---------------- [Here ∆P/Pₒ is referred as relative lowering in vapours pressure]
🔎📌 Short Reason
According to the third form of Raoult’s law, the relative lowering of vapour pressure is equal to the mole fraction of solute.
∆P/Pₒ = X₂ ---------------- [Here ∆P/Pₒ is referred as relative lowering in vapours pressure]
14: The sum of mole fractions of components of a solution is equal to:
a) 0.0
b) 1.0
c) 10
d) 100
✅ Correct Answer: (b) 1.0
🔎📌 Short Reason
The sum of mole fractions of components of a solution is equal to 1.0. By definition, mole fractions are ratios, so they are dimensionless and always between 0 and 1.
🔎📌 Short Reason
The sum of mole fractions of components of a solution is equal to 1.0. By definition, mole fractions are ratios, so they are dimensionless and always between 0 and 1.
15: How many mole of NaOH are present in 2dm³ of 1 molar aqueous solution of it.
a) 0.5 mole
b) 1 mole
c) 1.5 mole
d) 2 mole
✅ Correct Answer: (d) 2 mole
🔎📌 Short Reason
1 molar aqueous solution contains 1 mole of solute per 1 dm³. Hence 1 molar aqueous solution contains 2 mole per 2 dm³.
🔎📌 Short Reason
1 molar aqueous solution contains 1 mole of solute per 1 dm³. Hence 1 molar aqueous solution contains 2 mole per 2 dm³.
16: A colloidal solution of liquid into liquid is known as:
a) Gel
b) Foam
c) Sol
d) Emulsion
✅ Correct Answer: (d) Emulsion
🔎📌 Short Reason
A colloidal solution of liquid into liquid is known as Emulsion .
🔎📌 Short Reason
A colloidal solution of liquid into liquid is known as Emulsion .
17: An example of completely immiscible liquid pair is:
a) Benzene to toluene
b) Water and phenol
c) Water and Benzene
d) Water & methanol
✅ Correct Answer: (b) Water and phenol
🔎📌 Short Reason
Water and phenol is an example of completely immiscible liquid pair .
🔎📌 Short Reason
Water and phenol is an example of completely immiscible liquid pair .
18: A 15% W/W KOH solution can be prepared by mixing 15g KOH in:
a) 15g water
b) 85g water
c) 100g water
d) 115g water
✅ Correct Answer: (b) 85g water
🔎📌 Short Reason
The numerical value of percent concentration indicates amount of solute. The amount of solvent can be calculated by subtracting amount of solute from 100 (only in case of W/W % or V/V%). Hence 15% W/W KOH solution can be prepared by mixing 15g KOH in 85 g (100–15) water .
🔎📌 Short Reason
The numerical value of percent concentration indicates amount of solute. The amount of solvent can be calculated by subtracting amount of solute from 100 (only in case of W/W % or V/V%). Hence 15% W/W KOH solution can be prepared by mixing 15g KOH in 85 g (100–15) water .
19: Least entropy found in which of the following state of water:
a) Steam at 100°C
b) Liquid water at 25°C
c) Liquid water at 4°C
d) Ice at 0°C
✅ Correct Answer: (d) Ice at 0°C
🔎📌 Short Reason
Entropy, S, is a thermodynamic quantity and it is defined as the measure of the disorder or randomness in a system. The more “messed up” or “disorderly” or “messy” a system becomes, we say the entropy of the system increases.
The entropy of substances with different states are different since the arrangement of the molecules are different. Solids have the lowest entropy value among the other states of matter since the molecules in solids are stationary.
These molecules only vibrate but do not move due to the strong interactions. Their molecules are therefore more ordered than those in other states of matter. Thus among three states of matter, the randomness and also entropy follows the order:
Gas > liquid > solid ⇒ Sgas > Sliquid > Ssolid .
🔎📌 Short Reason
Entropy, S, is a thermodynamic quantity and it is defined as the measure of the disorder or randomness in a system. The more “messed up” or “disorderly” or “messy” a system becomes, we say the entropy of the system increases.
The entropy of substances with different states are different since the arrangement of the molecules are different. Solids have the lowest entropy value among the other states of matter since the molecules in solids are stationary.
These molecules only vibrate but do not move due to the strong interactions. Their molecules are therefore more ordered than those in other states of matter. Thus among three states of matter, the randomness and also entropy follows the order:
Gas > liquid > solid ⇒ Sgas > Sliquid > Ssolid .
20: Which of the following change is not an endothermic reaction
a) Combustion of butane
b) Cracking of alkanes
c) Decomposition of lime
d) Photosynthesis
✅ Correct Answer: (a) Combustion of butane
🔎📌 Short Reason
Combustion is always exothermic releasing heat called heat of combustion.
🔎📌 Short Reason
Combustion is always exothermic releasing heat called heat of combustion.
21: Heat transfer cannot be feasible across the boundary of a/an
a) Open system
b) Thermo permeable system
c) Isolated system
d) Close system
✅ Correct Answer: (c) Isolated system
🔎📌 Short Reason
Isolated system is an ideal thermodynamic system that does not allow either matter or heat transfer across the boundary .
🔎📌 Short Reason
Isolated system is an ideal thermodynamic system that does not allow either matter or heat transfer across the boundary .
22: In a thermochemical process, no work is done if the system is kept at:
a) Constant pressure
b) Constant temperature
c) Constant volume
d) Constant mass
✅ Correct Answer: (c) Constant volume
🔎📌 Short Reason
When a reaction is carried out at constant volume (ΔV = 0), no work is done on or by the system.
🔎📌 Short Reason
When a reaction is carried out at constant volume (ΔV = 0), no work is done on or by the system.
23: Standard enthalpy of formation of all of the following elements at 25°C and 1 atm pressure are zero except:
a) C(diamond)
b) C(graphite)
c) O₂
d) N₂
✅ Correct Answer: (a) C(diamond)
🔎📌 Short Reason
C(diamond) → not the most stable form of carbon at standard conditions. Its ΔHf° is positive (≈ +1.9 kJ/mol), because energy is required to convert graphite into diamond. Therefore, among the given options, only C(diamond) does not have zero standard enthalpy of formation.
🔎🧠 Step by Step Reasoning
Conventionally ΔHf° of most the elements (H₂, O₂, N₂, Na, graphite, rhombic sulphur etc.) are taken as zero because no further change is needed to bring them to standard state conditions. However, for those elements which exists in more than one allotropic forms, the most stable allotropic form is conventionally assumed to have ΔHf° = 0.
For example
⚡ΔHf° of graphite is taken as zero as it is thermodynamically more stable allotrope of carbon than diamond at 25°C & 1 atm
⚡O₂ is more stable allotropic form than O₃ (ozone) and therefore, ΔHf° of O₂ is assumed to be zero.
⚡Rhombic sulphur has ΔHf° = 0 as it is the most stable allotrope of sulphur.
.
🔎📌 Short Reason
C(diamond) → not the most stable form of carbon at standard conditions. Its ΔHf° is positive (≈ +1.9 kJ/mol), because energy is required to convert graphite into diamond. Therefore, among the given options, only C(diamond) does not have zero standard enthalpy of formation.
🔎🧠 Step by Step Reasoning
Conventionally ΔHf° of most the elements (H₂, O₂, N₂, Na, graphite, rhombic sulphur etc.) are taken as zero because no further change is needed to bring them to standard state conditions. However, for those elements which exists in more than one allotropic forms, the most stable allotropic form is conventionally assumed to have ΔHf° = 0.
For example
⚡ΔHf° of graphite is taken as zero as it is thermodynamically more stable allotrope of carbon than diamond at 25°C & 1 atm
⚡O₂ is more stable allotropic form than O₃ (ozone) and therefore, ΔHf° of O₂ is assumed to be zero.
⚡Rhombic sulphur has ΔHf° = 0 as it is the most stable allotrope of sulphur.
.
24: Volume is a:
a) State function
b) Colligative property
c) Intensive property
d) Path function
✅ Correct Answer: (a) State function
🔎📌 Short Reason
Volume is a state function as it depends upon initial and final states .
🔎📌 Short Reason
Volume is a state function as it depends upon initial and final states .
25: In the equation of First law of thermodynamics (∆E=q + w), the property(s) which depends upon initial and final state is (are):
a) ΔE
b) q
c) W
d) Both q and W
✅ Correct Answer: (a) ΔE
🔎📌 Short Reason
Only ΔE is a state function which depends upon initial and final state. The other two variables of the first law of thermodynamics i.e. q and W both are path functions that do not depend upon initial and final state.
🔎📌 Short Reason
Only ΔE is a state function which depends upon initial and final state. The other two variables of the first law of thermodynamics i.e. q and W both are path functions that do not depend upon initial and final state.
26: Which statement is incorrect?
a) For constant pressure process, ∆H = ΔE + P∆V
b) For constant volume process, ΔE = q
c) For exothermic reactions, ΔH > 0
d) For Hess law ΣΔH°(cycle) = 0
✅ Correct Answer: (c) For exothermic reactions, ΔH > 0
🔎📌 Short Reason
For exothermic reactions, heat is released to the surroundings, so enthalpy change is negative: ΔH < 0 .
🔎📌 Short Reason
For exothermic reactions, heat is released to the surroundings, so enthalpy change is negative: ΔH < 0 .
27: Which of the following enthalpy change is always positive?
a) Enthalpy of formation
b) Enthalpy of decomposition
c) Enthalpy of combustion
d) Enthalpy of reaction
✅ Correct Answer: (b) Enthalpy of decomposition
🔎📌 Short Reason
Enthalpy of decomposition is always positive as decomposition is always endothermic. Enthalpy of formation and Enthalpy of reaction may be positive or negative. Enthalpy of combustion is always negative
🔎📌 Short Reason
Enthalpy of decomposition is always positive as decomposition is always endothermic. Enthalpy of formation and Enthalpy of reaction may be positive or negative. Enthalpy of combustion is always negative
28: The outer body of dry cell serves as anode, it is made up of
a) Copper
b) Zinc
c) Lead
d) Iron
✅ Correct Answer: (b) Zinc
🔎📌 Short Reason
In a dry cell, the outer body is made of zinc, which acts as the anode. Zinc undergoes oxidation (loses electrons) during the cell reaction, while the carbon rod inside acts as the cathode.
🔎📌 Short Reason
In a dry cell, the outer body is made of zinc, which acts as the anode. Zinc undergoes oxidation (loses electrons) during the cell reaction, while the carbon rod inside acts as the cathode.
29: The conduction of electricity through an electrolytic solution is due to the flow of
a) Electrons
b) Ions
c) Atoms
d) Molecules
✅ Correct Answer: (b) Ions
🔎📌 Short Reason
The conduction of electricity through an electrolytic solution is called electrolytic conduction which is due to the movement of free floating ions of electrolyte. In contrast, the electronic or metallic conduction of electricity through metal or graphite is due to free moving valence electrons.
🔎📌 Short Reason
The conduction of electricity through an electrolytic solution is called electrolytic conduction which is due to the movement of free floating ions of electrolyte. In contrast, the electronic or metallic conduction of electricity through metal or graphite is due to free moving valence electrons.
30: During electrolysis, the reaction that takes place at anode is
a) Oxidation
b) Hydrolysis
c) Simultaneous oxidation and reduction
d) Reduction
✅ Correct Answer: (a) Oxidation
🔎📌 Short Reason
In electrochemical cells (whether electrolytic or Galvanic cell), oxidation always takes place at anode while reduction occurs at cathode.
🔎📌 Short Reason
In electrochemical cells (whether electrolytic or Galvanic cell), oxidation always takes place at anode while reduction occurs at cathode.
31: 27 g of Al will react completely with how many grams of oxygen (O₂)? Given reaction:
4Al + 3O₂→2Al₂O₃
a) 8 g
b) 40 g
c) 10 g
d) 24 g
✅ Correct Answer: (d) 24 g
🔎📌 Short Reason
Molar mass of Al = 27 g/mol So, 27 g Al = 1 mole .
Balanced equation: 4 mol Al reacts with 3 mol O₂ → 1 mol Al reacts with: ¾ mol O₂ (mole ratio)
Molar mass of O₂ = 32 g/mol So:
¾ × 32 = 24 g O
🔎📌 Short Reason
Molar mass of Al = 27 g/mol So, 27 g Al = 1 mole .
Balanced equation: 4 mol Al reacts with 3 mol O₂ → 1 mol Al reacts with: ¾ mol O₂ (mole ratio)
Molar mass of O₂ = 32 g/mol So:
¾ × 32 = 24 g O
32: The number of atoms is greatest in:
a) 24 g of ozone
b) 40 g of calcium
c) 127 g of iodine
d) 4 g of hydrogen
✅ Correct Answer: (d) 4 g of hydrogen
🔎📌 Short Reason
Ozone → 9.033 × 10²³ atoms Calcium → 6.022 × 10²³ atoms Iodine → 6.022 × 10²³ atoms Hydrogen → 2.408 × 10²⁴ atoms 👉 The greatest number of atoms is in 4 g of hydrogen.6.
🔎🧠 Step by Step Reasoning
(a) 24 g of ozone (O₃)
Molar mass of O₃ = 48 g/mol
Moles = 24/48 = 0.5 mol
Molecules = 0.5× 6.022×10²³ = 3.011×10²³
Each molecule has 3 atoms →
Atoms = Molecules x atomicity = 3.011 ×10²³ × 3 = 9.033×10²³ atoms
(b) 40 g of calcium (Ca)
Atomic mass = 40 g/mol
Moles = 40/40 =1 mol
Atoms = 1 × 6.022×10²³ = 6.022×10²³ atoms
(c) 127 g of iodine (I₂)
Molar mass of I₂ = 254 g/mol
Moles = 127/254=0.5 mol
Molecules = 0.5 × 6.022×10²³ = 3.011 × 10²³
Each molecule has 2 atoms →
Atoms = Molecules x atomicity = 3.011 × 10²³ × 2 = 6.022 × 10²³ atoms
(d) 4 g of hydrogen (H₂)
Molar mass of H₂ = 2 g/mol
Moles = 4/2 = 2 mol
Molecules = 2 × 6.022 × 10²³ = 1.204 × 10²⁴
Each molecule has 2 atoms →
Atoms = Molecules x atomicity = 1.204 × 10²⁴ × 2 = 2.408×10²⁴ atoms → greatest number of atoms✅
.
🔎📌 Short Reason
Ozone → 9.033 × 10²³ atoms Calcium → 6.022 × 10²³ atoms Iodine → 6.022 × 10²³ atoms Hydrogen → 2.408 × 10²⁴ atoms 👉 The greatest number of atoms is in 4 g of hydrogen.6.
🔎🧠 Step by Step Reasoning
(a) 24 g of ozone (O₃)
Molar mass of O₃ = 48 g/mol
Moles = 24/48 = 0.5 mol
Molecules = 0.5× 6.022×10²³ = 3.011×10²³
Each molecule has 3 atoms →
Atoms = Molecules x atomicity = 3.011 ×10²³ × 3 = 9.033×10²³ atoms
(b) 40 g of calcium (Ca)
Atomic mass = 40 g/mol
Moles = 40/40 =1 mol
Atoms = 1 × 6.022×10²³ = 6.022×10²³ atoms
(c) 127 g of iodine (I₂)
Molar mass of I₂ = 254 g/mol
Moles = 127/254=0.5 mol
Molecules = 0.5 × 6.022×10²³ = 3.011 × 10²³
Each molecule has 2 atoms →
Atoms = Molecules x atomicity = 3.011 × 10²³ × 2 = 6.022 × 10²³ atoms
(d) 4 g of hydrogen (H₂)
Molar mass of H₂ = 2 g/mol
Moles = 4/2 = 2 mol
Molecules = 2 × 6.022 × 10²³ = 1.204 × 10²⁴
Each molecule has 2 atoms →
Atoms = Molecules x atomicity = 1.204 × 10²⁴ × 2 = 2.408×10²⁴ atoms → greatest number of atoms✅
.
33: If Nᴀ is Avogadro’s number, then the number of valence electrons in 4.2 g of nitride ion (N³⁻) is:
a) 2.4Nᴀ
b) 4.2Nᴀ
c) 1.6Nᴀ
d) 3.2Nᴀ
✅ Correct Answer: (a) 2.4 Nᴀ
🔎📌 Short Reason
4.2 g of N³⁻ = 0.3 mol ions. Each ion has 8 valence electrons. Multiply → 2.4Nᴀ.
🔎📌 Short Reason
4.2 g of N³⁻ = 0.3 mol ions. Each ion has 8 valence electrons. Multiply → 2.4Nᴀ.
34: 30 litres of each CS₂ and oxygen are heated in a vessel. What volume of CO₂ could be produced at end of the reaction? CS₂ + 3O₂ → CO₂ + 2SO₂
a) 15L
b) 10 L
c) 20L
d) 30L
✅ Correct Answer: (b) 10 L
🔎📌 Step by Step Reasoning
Balanced equation: CS₂ + 3O₂ → CO₂ + 2SO₂
Given: 30 L CS₂ and 30 L O₂
Limiting reagent: Required O₂ for 30 L CS₂ = 3 × 30 L = 90 L O₂
Available O₂: 30 L → O₂ is limiting.
Extent of reaction (based on limiting O₂):
Reacted CS₂ = 30 L O₂/3 = 10 L CS₂
Volume of CO₂ produced (1:1 with CS₂): CO₂ = 10 L
🔎📌 Step by Step Reasoning
Balanced equation: CS₂ + 3O₂ → CO₂ + 2SO₂
Given: 30 L CS₂ and 30 L O₂
Limiting reagent: Required O₂ for 30 L CS₂ = 3 × 30 L = 90 L O₂
Available O₂: 30 L → O₂ is limiting.
Extent of reaction (based on limiting O₂):
Reacted CS₂ = 30 L O₂/3 = 10 L CS₂
Volume of CO₂ produced (1:1 with CS₂): CO₂ = 10 L
35: The number of atoms in 16 g of methane (CH₄) is:
a)3.01 × 10²³
b) 3.01 × 10²⁴
c) 30.1 × 10²⁴
d) None of these
✅ Correct Answer: (b) 3.01 × 10²⁴
🔎📌 Short Reason
16 g CH₄ = 1 mol → 6.022 × 10²³ molecules. Each molecule has 5 atoms → total = 3.01 × 10²⁴ atoms.
🔎📌 Short Reason
16 g CH₄ = 1 mol → 6.022 × 10²³ molecules. Each molecule has 5 atoms → total = 3.01 × 10²⁴ atoms.
36: A certain gaseous mixture contains methane and sulhur dioxide in ratio of 1:8 by mass. The ratio of the number of molecules is
a) 1:8
b) 1:2
c) 1:1
d) 2:1
✅ Correct Answer: (b) 1:2
🔎📌 Short Reason
Mass ratio 1:8 converts to mole ratio 1:2 because CH₄ has smaller molar mass (16 g/mol) compared to SO₂ (64 g/mol). Hence, the number of molecules ratio is 1:2.
🔎🧠 Step by Step Reasoning
Assume the mass of CH₄ is 1 g and that of SO₂ is 8 g
nᴄʜ₄ = 1g/16 gmol⁻¹ = 1/16 mol or 0.0625 mol
nᵴᴏ₂ = 8g/64 gmol⁻¹ = 1/8 mol or 0.125 mol
The ratio of number of molecules of two substances is same as that of number of moles.
Ratio of number of moles of CH₄ to SO₂ (same as mole ratio) = 1/16 : 1/8 (0.0625:0.125) = 1:2
Ratio of number of molecules of CH₄ to SO₂ = 1:2
🔎📌 Short Reason
Mass ratio 1:8 converts to mole ratio 1:2 because CH₄ has smaller molar mass (16 g/mol) compared to SO₂ (64 g/mol). Hence, the number of molecules ratio is 1:2.
🔎🧠 Step by Step Reasoning
Assume the mass of CH₄ is 1 g and that of SO₂ is 8 g
nᴄʜ₄ = 1g/16 gmol⁻¹ = 1/16 mol or 0.0625 mol
nᵴᴏ₂ = 8g/64 gmol⁻¹ = 1/8 mol or 0.125 mol
The ratio of number of molecules of two substances is same as that of number of moles.
Ratio of number of moles of CH₄ to SO₂ (same as mole ratio) = 1/16 : 1/8 (0.0625:0.125) = 1:2
Ratio of number of molecules of CH₄ to SO₂ = 1:2
37: Which of the following represents 1 g molecule of the substance?
a) 6.02 × 10²³ molecules NH₃
b) 4 g of helium
c) 40 g of calcium oxide
d) both a and b
✅ Correct Answer: (d) both a and b
🔎📌 Short Reason
NH₃: 1 mole = 6.022 × 10²³ molecules.
He: 4 g = 1 mole atoms. This represents 1 g atom (same as 1 g molecule for monoatomic gases).
Both satisfy the definition of 1 g molecule.
🔎📌 Short Reason
NH₃: 1 mole = 6.022 × 10²³ molecules.
He: 4 g = 1 mole atoms. This represents 1 g atom (same as 1 g molecule for monoatomic gases).
Both satisfy the definition of 1 g molecule.
38: Which of the following does not occupy a volume of 4.48 L at STP?
a) 0.2 mol of H₂
b) 12.8 g of SO₂
c) 800 mg of He
d) 3.2 g of O₂
✅ Correct Answer: d) 3.2 g of O₂
🔎📌 Short Reason
At STP, 0.2 mol of any gas = 4.48 L. Options (a), (b), and (c) all equal 0.2 mol. But 3.2 g O₂ = 0.1 mol → 2.24 L, so it does not occupy 4.48 L.
🔎📌 Short Reason
At STP, 0.2 mol of any gas = 4.48 L. Options (a), (b), and (c) all equal 0.2 mol. But 3.2 g O₂ = 0.1 mol → 2.24 L, so it does not occupy 4.48 L.
39: Which of the following ionic compound contains largest number of ions?
a) 0.1 mol of KI
b) 0.1 mol of AlPO₄
c) 11.1 g of CaCl₂
d) 0.1 mol of SrCO₃
✅ Correct Answer: c) 11.1 g of CaCl₂
🔎📌 Short Reason
11.1 g CaCl₂ = 0.1 mol → 3 ions per formula unit → 0.3 Nₐ ions, which is greater than the 0.2 Nₐ ions from the other compounds.
🔎📌 Short Reason
11.1 g CaCl₂ = 0.1 mol → 3 ions per formula unit → 0.3 Nₐ ions, which is greater than the 0.2 Nₐ ions from the other compounds.
40: A metal “M” reacts with “S” to form “MS”. If 3.6g of M reacts with 0.09 mole of sulphur, then what is the name of metal “M”?
a) Cr
b) Mg
c) Ca
d) Mn
✅ Correct Answer: (c) Ca
🔎📌 Short Reason
3.6 g of M corresponds to 0.09 mol → molar mass = 40 g/mol → matches calcium
🔎🧠 Step by Step Reasoning
Reaction type: MS means 1 atom of M reacts with 1 atom of S
🔎📌 Short Reason
3.6 g of M corresponds to 0.09 mol → molar mass = 40 g/mol → matches calcium
🔎🧠 Step by Step Reasoning
Reaction type: MS means 1 atom of M reacts with 1 atom of S
Stoichiometrically,
M:S → 1mol : 1 mol, So → 0.09 mol : 0.09mol
Moles of sulphur given: 0.09 mol S
Moles of M = 0.09 mol
Mass of M given: 3.6 g
Molar mass of M:
No. of mole = m/M and M (Molar mass) = m/n = 3.6/0.09 = 40 g (Ca has molar mass of 40g/mol)
Which element has atomic mass ≈ 40?
Cr = 52
Mg = 24
Ca = 40
Mn = 55
👉 The metal is Calcium (Ca).
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