🔥🌟 MDCAT/ECAT/FSC Grand Chemistry MCQs Quiz # 8 (Advance Level) | Interactive Quiz 🧪💡| Learn & Practice!

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1: The value of solubility product depends only on

a) Solvent

b) Catalyst

c) Temperature

d) Pressure

✅ Correct Answer: (c) Temperature

🔎📌 Short Reason

Solubility product is an equilibrium constant, and equilibrium constants are functions of temperature only. Changes in solvent, catalyst, or pressure do not alter the intrinsic Kₛₚ value
🔎🧠 Step by Step Reasoning
🔎Kₛₚ is an equilibrium constant for the dissolution of a sparingly soluble salt.
🔎Like all equilibrium constants, its value depends only on temperature.
🔎It does not depend on solvent (though solubility itself can vary with solvent), catalyst (irrelevant here), or pressure (important for gases, but salts are solids).

2: The unit in which wave number is measured:

a) sec⁻¹

b) hertz

c) cm⁻¹

d) nanometer

✅ Correct Answer: (c) cm⁻¹

🔎📌 Short Reason

Wave number is the reciprocal of wavelength, so its unit is per centimeter (cm⁻¹).
🔎🧠 Step by Step Reasoning
Wave number (ν̅ = nu̅) is defined as the reciprocal of wavelength:
Since wavelength (λ) is usually expressed in centimeters, the unit of wave number becomes cm⁻¹
Other options:
sec⁻¹ → unit of frequency (not wave number)
hertz (Hz) → also frequency (s⁻¹)
nanometer → unit of wavelength, not wave number

3: A line in Pfund series is obtained when an electron from higher energy levels returns to

a) 1st orbit

b) 5th orbit

c) 3rd orbit

d) 6th orbit

✅ Correct Answer: (b) 5th orbit

🔎📌 Short Reason

The Pfund series is part of the hydrogen emission spectrum. It arises when electrons drop from higher energy levels (n ≥ 6) down to n = 5
🔎🧠 Step by Step Reasoning
Hydrogen spectral series are defined by the final orbit (n) to which the electron falls:
📌Lyman series → electron falls to n = 1
📌Balmer series → electron falls to n = 2
📌Paschen series → electron falls to n = 3
📌Brackett series → electron falls to n = 4
📌Pfund series → electron falls to n = 5
👉🏼So, Pfund series corresponds to transitions ending at the 5th orbit.

4: The energy of an electron in Bohr’s atom ……….. as we move away from the nucleus:

a) Increases

b) Decreases

c) Remains same

d) Unpredicted

✅ Correct Answer: (a) Increases

🔎📌 Short Reason

In Bohr’s atom, electron energy is negative and increases toward zero as the electron moves away from the nucleus. Hence, energy increases with distance.
🔎🧠 Step by Step Reasoning
📌 The energy of an electron in the nth Bohr’s orbit is given by: Eₙ = −13.6/n² eV
📌As n increases (electron moves farther from the nucleus):
📌The denominator n² increases.
📌The negative value becomes less negative (closer to zero).
📌This means the electron’s energy increases (approaches 0).
⚛️Physically:
📌Near the nucleus → electron is strongly bound → lower energy (more negative).
📌Farther away → electron is less bound → higher energy (less negative).

5: The energy of an electron in the first orbit in hydrogen atom is −313.6/n² kcalmol⁻¹. The energy of electron in 3rd orbit is given by:

a) −313.6/3 kcal mol⁻¹

b) −313.6/9 kcal mol⁻¹

c) −313.6/2 kcal mol⁻¹

d) −313.6 × 3 kcal mol⁻¹

✅ Correct Answer: (b) −313.6/9 kcal mol⁻¹
🔎📌 Short Reason
Energy in Bohr’s atom decreases in magnitude as n increases.
For n = 3, substitute into the formula → −313.6/9.
🔎🧠 Step by Step Reasoning
📌 Formula:
📌 For nth orbit: Eₙ = −313.6/n²
📌 For n = 3: E₃ = −313.6/3²
📌 Simplify: E₃ = −313.6/9 kcal mol⁻¹

6: The radius of the first orbit in hydrogen atom is 0.529 Å. The radius of the second orbit is:

a) ½ × 0.529 Å

b) 2 × 0.529 Å

c) 8 × 0.529 Å

d) 4 × 0.529 Å

✅ Correct Answer: (d) 4 × 0.529 Å
🔎📌 Short Reason
Bohr’s formula shows orbit radius increases with n².
For n = 2, radius = 4 × 0.529 Å = 2.116 Å.
🔎🧠 Step by Step Reasoning
📌 The radius of the nth Bohr’s orbit is: rₙ = n²⋅r₁ (where r₁ =0.529 Å).
📌 For n = 2: r₂ = 2²⋅r₁ = 4⋅r₁ = 4 ⋅ 0.529 Å= 2.116 Å
📌 Numerical value: r₂ = 2.116 A˚

7: Electromagnetic radiations with minimum wavelength are:

a) Ultraviolet

b) X rays

c) Infrared

d) Radiowave

✅ Correct Answer: (b) X rays
🔎📌 Short Reason
In the electromagnetic spectrum, X rays lie between ultraviolet and gamma rays. They have much shorter wavelength than UV, IR, or radiowaves, so they represent the minimum wavelength among the given choices.
🔎🧠 Step by Step Reasoning
🔎Electromagnetic spectrum order (increasing wavelength):
Gamma rays < X rays < Ultraviolet < Visible < Infrared < Microwaves < Radiowaves
📌 Minimum wavelength → highest energy radiation.
🔎 Among the given options:
📌 Ultraviolet: shorter than visible, but longer than X rays
📌 Infrared: longer than visible
📌 Radiowaves: longest wavelength
📌 X rays: shorter wavelength than UV, IR, and radiowaves
👉 Therefore, X rays have the minimum wavelength among the listed options.

8: The strongest oxidizing agent in the electro chemical series is:

a) Li

b) F

c) H₂

d) Cu

✅ Correct Answer: (b) F
🔎📌 Short Reason
The strongest oxidizing must have highest reduction potential. In ECS, F has the highest reduction potential, therefore fluorine is the strongest oxidizing agent.

9: Galvanized rod of iron is coated with:

a) Nickel

b) Chromium

c) Carbon

d) Zinc

✅ Correct Answer: (d) Zinc
🔎📌 Short Reason
Galvanized iron is coated with zinc. Galvanizing is the type of electroplating involving coating of zinc on baser metals like iron.

10: Oxidation number of Cr in Na₂Cr₂O₇, is:

a) +3

b) +8

c) +6

d) +12

✅ Correct Answer: (c) +6
🔎📌 Short Reason
In Na₂Cr₂O₇ → 2(+1) + 2x + 7(−2) = 0 ⇒ 2x = 12 ⇒ x = +6.
🔎🧠 Step by Step Reasoning
📌 Oxidation number of Na = +1
📌 Oxidation number of O = −2
📌 In a neutral compound, sum of oxidation numbers of all atoms is equal to zero.
2(Na) + 2Cr + 7(O) = 0
2(+1) + 2Cr + 7(−2) = 0
2 + 2Cr + (−14) = 0
2 + 2Cr −14 = 0
2Cr −12 = 0
2Cr = +12
👉 Cr = +12/2 = +6