Which of the following pairs is the chain isomer?

Options

A.
B.
C.
D.

Explanation

To determine which of the given pairs are chain isomers, we need to understand what chain isomers are. Chain isomers are compounds that have the same molecular formula but differ in the arrangement of the carbon skeleton. Here’s how to approach the problem step by step:

### Step-by-Step Solution:

1. **Identify the Molecular Formula**:
- For each pair given in the question, write down the molecular formula of each compound.

2. **Draw the Structures**:
- Draw the structural formulas of each compound in the pair. This will help visualize the arrangement of carbon atoms.

3. **Count the Carbon Atoms**:
- Count the number of carbon atoms in the longest continuous chain for each compound. This will help identify if they differ in their carbon skeleton.

4. **Compare the Carbon Skeletons**:
- Check if the main carbon chain differs between the two compounds. If they have the same number of carbon atoms but different arrangements of those carbon atoms, they are chain isomers.

5. **Identify the Correct Pair**:
- From your comparisons, identify which pair has different carbon skeletons, confirming they are chain isomers.

### Example Analysis:

Let’s assume we have the following pairs (hypothetical examples):

- **Pair A**: C5H12 (n-pentane) and C5H12 (isopentane)
- **Pair B**: C6H14 (hexane) and C6H14 (2-methylpentane)
- **Pair C**: C4H10 (butane) and C4H10 (isobutane)
- **Pair D**: C3H8 (propane) and C3H8 (propene)

1. **Identify the Molecular Formula**:
- All pairs have the same molecular formula.

2. **Draw the Structures**:
- For example, n-pentane has a straight chain, while isopentane has a branched chain.

3. **Count the Carbon Atoms**:
- For Pair A: Both have 5 carbons.
- For Pair B: Both have 6 carbons.
- For Pair C: Both have 4 carbons.
- For Pair D: Both have 3 carbons.

4. **Compare the Carbon Skeletons**:
- Pair A: Same formula, different structures (chain isomers).
- Pair B: Same formula, different structures (chain isomers).
- Pair C: Same formula, different structures (chain isomers).
- Pair D: Same formula, but propene is not an isomer of propane.

5. **Identify the Correct Pair**:
- The pairs that qualify as chain isomers are A, B, and C.

### Final Answer:
Based on the analysis, the pair that is chain isomers is **Pair B** (if it was the only one that differed in the longest chain).