Which of the following pairs of compounds are functional isomers?

Options

A.
B.
C.
D.

Explanation

To determine which pairs of compounds are functional isomers, we need to follow a systematic approach. Functional isomers are compounds that have the same molecular formula but different functional groups. Here’s a step-by-step solution to the question:

### Step 1: Understand the Definition of Functional Isomers
Functional isomers are compounds that have the same molecular formula but differ in the functional groups present. This means that while the number and types of atoms are the same, the way these atoms are arranged into functional groups is different.

**Hint:** Remember, the key to identifying functional isomers is to check both the molecular formula and the functional groups.

### Step 2: Analyze Each Pair of Compounds
We will analyze each pair of compounds given in the question to see if they meet the criteria for functional isomerism.

1. **First Pair:**
- Check the molecular formula of both compounds.
- Identify the functional groups present (e.g., ketones, alcohols).
- If both compounds have the same functional group (e.g., both are ketones), they are not functional isomers.

**Hint:** Look for changes in functional groups. If they remain the same, they are not functional isomers.

2. **Second Pair:**
- Again, check the molecular formula.
- Identify the functional groups.
- If one compound has an extra atom (like oxygen), they cannot be functional isomers.

**Hint:** Ensure both compounds have identical molecular formulas before concluding.

3. **Third Pair:**
- Identify the functional groups in both compounds.
- If both compounds are esters, they are not functional isomers.

**Hint:** Functional isomers must have different functional groups, so look for any differences.

4. **Fourth Pair:**
- Check if one compound is an ester and the other is a ketone or ether.
- If they have different functional groups and the same molecular formula, they are functional isomers.

**Hint:** This is the critical step where you identify the change in functional groups.

### Step 3: Conclusion
After analyzing all pairs, we find that the last option (the fourth pair) shows a transition from one functional group (ester) to another (ketone/ether). Therefore, they are functional isomers.

**Final Answer:** The correct answer is option D, as it represents functional isomers.