Two neighbours of homologous series differ by

Options

A. `CH`
B. `CH_2`
C. `CH_3`
D. `CH_4`

Explanation

To answer the question "Two neighbours of homologous series differ by," we can follow these steps:

### Step 1: Understand the concept of a homologous series
A homologous series is a group of organic compounds that have the same functional group and similar chemical properties, but differ by a specific structural unit.

### Step 2: Identify the structural unit that differentiates the neighbours
In a homologous series, each successive compound differs from the previous one by a specific number of carbon and hydrogen atoms. This unit is typically a -CH2- group, which means each compound in the series has one more carbon atom and two more hydrogen atoms than the previous compound.

### Step 3: Write the general formula
The general formula for alkanes (a type of homologous series) is CnH2n+2. For alkenes, it is CnH2n, and for alcohols, it is CnH2n+1OH. The key point is that the difference between two consecutive members is -CH2-.

### Step 4: Conclusion
Thus, the two neighbours of a homologous series differ by a -CH2- group.

### Final Answer
The two neighbours of a homologous series differ by -CH2-.

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