Which statement correctly describes a key feature of a homologous series?

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The correct answer is A. A homologous series is a group of organic compounds where:

1. Each successive member differs by one $	ext{CH}_2$ unit (equivalent to 14 mass units in molar mass).

2. All members have the same general formula (for example, alkanes are $	ext{C}_n	ext{H}_{2n+2}$).

3. Members share the same functional group and therefore show similar chemical properties (for example, all alcohols undergo oxidation and esterification reactions in comparable ways).

4. Physical properties (such as boiling point, melting point, and density) show a gradual variation as the molar mass increases.

Example: The alkane homologous series includes methane ($	ext{CH}_4$), ethane ($	ext{C}_2	ext{H}_6$), propane ($	ext{C}_3	ext{H}_8$), and butane ($	ext{C}_4	ext{H}_{10}$). Each successive member differs by $	ext{CH}_2$ and boiling points increase gradually: $-162°	ext{C}$, $-89°	ext{C}$, $-42°	ext{C}$, and $-1°	ext{C}$ respectively.

Describe the features of a homologous series.

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