🔥🌟 MDCAT/ECAT/FSC/XII Grand Chemistry MCQs Interactive Quiz # 4 🧪💡 | Learn & Practice!

 

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1. The number of isomers of hexane are

a) 3

b) 5

c) 9

d) 18

✅ Correct Answer: (b) 5
👉 Hexane (C₆H₁₄) is an alkane having 5 structural isomers due to different branching patterns i.e n Hexane, 2 Methylpentane, 3 Methylpentane, 2,2 Dimethylbutane and 2,3 Dimethylbutane

2. Cycloalkenes have the general formula:

a) CₙH₂ₙ

b) CₙH₂ₙ₊₂

c) CₙH₂ₙ₋₂

d) CₙH₂ₙ₊₄

✅ Correct Answer: (c) CₙH₂ₙ₋₂
👉 Cycloalkenes have one double bond in the ring, reducing 2 hydrogens from CₙH₂ₙ (cycloalkanes) making its general formula CₙH₂ₙ₋₂. (Cycloalkanes → CₙH₂ₙ (like alkanes but cyclic).

3. The functional group in RCN is

a) Thioalcohol

b) Ether

c) Nitrile

d) Thioether

✅ Correct Answer: (c) Nitrile
👉 RCN or R–C≡N (where carbon is triple bonded to nitrogen) is the general formula nitrile (alkanenitrile). The CN group is called the nitrile or cyano group.
👉 Thioalcohols (SH), ethers (-O-), and thioethers (-S-) involve oxygen/sulfur, not a C≡N bond.

4. Propanone and propanal are

a) Functional isomers

b) Positional isomers

c) Tautomers

d) Metamers

✅ Correct Answer: (a) Functional isomers
👉 Propanone (CH₃–CO–CH₃) → ketone. 👉 Propanal (CH₃–CH₂–CHO) → aldehyde. 👉 Same molecular formula (C₃H₆O) but different functional groups (aldehyde vs ketone). That makes them functional isomers.

5. The oxidation states of the elements of group VA is:

a) +1 and +3

b) −3 and −5

c) −3, +3 and +5

d) +1, −1 and +3

✅ Correct Answer: (c) −3, +3 and +5
👉 Group VA elements (N, P, As, Sb, Bi) exhibit −3, +3, and +5 oxidation states.
🔥 Example: Nitrogen in NH₃ → −3.
🔥Phosphorus in PCl₃ → +3.
🔥Phosphorus in PCl₅ → +5.

6. Which of the following s block elements form normal oxide when burnt in air?

a) Sr

b) Na

c) K

d) Li

✅ Correct Answer: (d) Li
👉 Lithium forms normal oxide (Li₂O) when burnt in air, unlike Na, K, or Sr which form peroxides/superoxides.

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