NEET Practice Questions (MCQs) with Answers & Solutions

A homologous series is a group of organic compounds that have a similar general formula, similar chemical properties, and successive members differ by a CH2 unit. Option o4 includes $CH_3COOH$ (acetic acid), $CH_3COOCH_3$ (methyl acetate), and $CH_3COOCH_2CH_3$ (ethyl acetate), which do not fit the criteria of a homologous series because they belong to different functional groups (carboxylic acid and esters).

In a homologous series, the compounds share a general formula. For example, alkanes have the general formula $C_nH_{2n+2}$, alkenes have $C_nH_{2n}$, and alcohols have $C_nH_{2n+1}OH$. This general formula helps in predicting the molecular formula of the compounds in the series.

In a homologous series, the physical properties of the compounds, such as boiling and melting points, gradually change with an increase in molecular mass. Thus, they do not have identical physical properties. The similar chemical properties and the ability to be represented by a general formula are true characteristics of a homologous series.

The molecular formula $C_5H_{12}$ corresponds to pentane, which has three chain isomers: n-pentane, isopentane (methylbutane), and neopentane (dimethylpropane).

2-chlorobutane and 3-chlorobutane are positional isomers because they differ in the position of the chlorine atom on the carbon chain. In 2-chlorobutane, the chlorine is attached to the second carbon, while in 3-chlorobutane, it is attached to the third carbon.