BPSC PGT CHEMISTRY-Classification of Organic Compounds

1. The successive members of a homologous series differ by an unit of which of the following?
a) –CH₃
b) CH₃CH₃
c) –CH₂
d) –CH₂CH₃

Answer: c
Explanation: In a homologous series, each successive member differs by a –CH₂– unit. For example, methanol (CH₃OH), ethanol (CH₃CH₂OH), and propanol (CH₃CH₂CH₂OH) clearly show that each compound in the series varies from the next by one CH₂ group.

2. Tropolone is a benzenoid compound.
a) True
b) False

Answer: b
Explanation: Tropolone is classified as a non-benzenoid compound because it lacks a benzene ring. In contrast, benzenoid compounds are those that contain one or more benzene rings, such as benzene, aniline, and naphthalene.

3. What is the other name for acyclic compounds?
a) Aliphatic
b) Aromatic
c) Heterocyclic
d) Alicyclic

Answer: a
Explanation: Acyclic or open-chain compounds are known as aliphatic compounds, consisting of straight or branched chains. On the other hand, aromatic, heterocyclic, and alicyclic compounds are closed-chain or ring structures.

4. Which of these is not an aliphatic compound?
a) Acetic acid
b) Acetaldehyde
c) Ethane
d) Tetrahydrofuran

Answer: d
Explanation: Tetrahydrofuran (CH₂)₄O is a closed-chain (ring) compound, whereas acetic acid, acetaldehyde, and ethane are open-chain compounds and thus classified as aliphatic.

5. Pick out the option that is not a functional group from the following.
a) Hydroxyl group
b) Benzene group
c) Aldehyde group
d) Carboxylic acid group

Answer: b
Explanation: The benzene ring is not considered a functional group. Functional groups are specific atoms or groups of atoms bonded in a particular way that determine the chemical properties of an organic compound. Examples include the hydroxyl group (-OH), aldehyde group (-CHO), and carboxyl group (-COOH), all of which alter the chemical behavior of hydrocarbon chains.