🔥🌟 MDCAT/ECAT/FSC Grand Chemistry MCQs Interactive Quiz # 2 🧪💡 | Learn & Practice!

 

1. The potential energy of an electron can be denoted by:

a Ze² / 8πε₀r

b -Ze² / 8πε₀r

c -Ze² / 4πε₀r

d None of them

Correct Answer: (b)

The potential energy (PE) of an electron in a hydrogen-like atom is negative, because the electron is bound to the nucleus. From Coulomb’s law and Bohr model: PE = − Ze²/8πε₀r Positive sign would indicate repulsion, so option (a) and (c) are incorrect.

2. If the volume occupied by oxygen gas (O₂) at STP is 44.8dm³, the number molecules of O₂ in the vessels are:

a 3.01 x 10²³

b 12.04 x 10²³

c 6.02 x 10²³

d 24.08 x 10²³

Correct Answer: (b)

Number of moles of O₂ = 44.8 dm³/22.4 dm³/mol = 2 mol 

Number of molecules = 2 mol × 6.022×10²³ molecules/mol = 12.04×10²³ molecules

3. The number of carbon atoms in half mole of sugar (C₁₂H₂₂O₁₁) are approximately:

a 6 x 10²³

b 36 x 10²³

c 60 x 10²³

d 72 x 10²³

Correct Answer: (b)

No. of atoms = n x Nᴀ x atomicity = 0.5 x 6.02 x 10²³ x 12 = 36.12 x 10²³

4. Significant figures in 0.0080900 are

a Four

b Three

c Seven

d Five

Correct Answer: (d)

The number 0.0080900 has five significant figures. 

Here's why: 

Leading zeros (before 8) are not significant. 

8, 9 are non-zero digits, so they are significant. 

The trailing zeros after 9 (in the decimal part) are significant because they appear after the decimal point. 

So, the significant figures are 8, 9, 0, 0, 0, which gives a total of five significant figures.

5. This molecule has zero dipole moment

a CCl₄

b CO₂

c Both a and b

d SO₂

Correct Answer: (c)

🔎 CCl₄ and CO₂ are highly symmetrical molecules, so their bond dipoles cancel out, giving zero dipole moment. SO₂ is bent, so it has a net dipole.

6. The number of bonds in ethene (C₂H₄) is:

a 5 sigma, 1 pi

b 5 sigma, 2 pi

c 3 sigma, two pi

d 7 sigma, 1 pi

Correct Answer: (a)

🔎 Ethene has a double bond between carbons (1 sigma + 1 pi) and four C–H sigma bonds, giving 5 sigma and 1 pi bonds.

7. The number of orbitals in 3rd energy level is

a 4

b 16

c 9

d 32

Correct Answer: (c)

🔎 The number of orbitals in any shell is 2n². For n = 3, that gives 9 (3²) orbitals.

8. This molecule has minimum bond angle

a CS₂

b NH₃

c H₂S

d BF₃

Correct Answer: (c)

🔎 H₂S is bent with a bond angle (92°) much smaller than NH₃ (107°) or BF₃ (120°), and CS₂ is linear (180°). Hence, H₂S has the minimum bond angle.

9. According to Hund’s rule the electronic configuration of carbon (C = 6) is:

a 1s² ,2s² 2pₓ¹ 2pᵧ²

b 1s² ,2s² 2pₓ¹ 2pᵧ¹

c 1s² ,2s² 2pₓ¹ 2pᵧ¹ 2pz¹

d 1s² ,2s² 2pₓ²

Correct Answer: (b)

🔎 Hund’s Rule states that electrons fill degenerate orbitals singly first. Thus, carbon’s ground-state configuration is 1s² 2s² 2pₓ¹ 2pᵧy¹.

10. Under similar conditions CH₄ gas diffuses faster than SO₂ gas:

a 1.5 times

b 16 times

c 4 times

d 2 times

Correct Answer: (d)

CH₄ diffuses faster than SO₂ because its molar mass is lower. 

Using Graham's law: 

Molar mass of CH₄ = 16 

Molar mass of SO₂ = 64 

The ratio of diffusion rates is the square root of the ratio of the molar masses: 

Rate of CH₄ = √64÷16 = √4 = 2 

So, CH₄ diffuses 2 times faster than SO₂.

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