Which of the following shows functional isomerism?

Options

A. `CH_(3)CH_(2)Cl` and `CH_(3)CH_(2)Br`
B. `CH_(3)CH_(2)Br` and `CH_(2)BrCH_(2)Br`
C. `C_(2)H_(5)OC_(2)H_(5)` and `CH_(3)OC_(3)H_(7)`
D. `CH_(3)CH_(2)CHO` and `CH_(3)COCH_(3)`

Explanation

To determine which of the given compounds shows functional isomerism, we need to analyze each option based on the definition of functional isomerism. Functional isomerism occurs when compounds have the same molecular formula but different functional groups.

### Step-by-Step Solution:

1. **Identify the Compounds**:
We have four parts (A, B, C, D) to analyze. Each part represents a different compound or set of compounds.

2. **Analyze Part A**:
- Compounds: CH3CH2Cl and CH3CH2Br
- Both compounds have the same molecular formula (C2H5X where X is Cl or Br).
- However, they differ only in the halogen atom (Cl vs. Br), which does not change the functional group.
- **Conclusion**: Does not show functional isomerism.

3. **Analyze Part B**:
- Compounds: CH3CH2Br and CH2BrCH2Br
- The first compound has one Br, while the second has two Br atoms.
- They have different molecular formulas (C2H5Br vs. C2H4Br2).
- **Conclusion**: Does not show isomerism as they are different compounds.

4. **Analyze Part C**:
- Compounds: C2H5O-C2H5 (ether) and CH3O-C3H7 (another ether).
- Both compounds are ethers and have the same functional group (ether).
- **Conclusion**: Does not show functional isomerism.

5. **Analyze Part D**:
- Compounds: CH3CH2CHO (aldehyde) and CH3COCH3 (ketone).
- Both compounds have the same molecular formula (C3H6O) but different functional groups (aldehyde vs. ketone).
- **Conclusion**: Shows functional isomerism.

6. **Final Answer**:
- The correct option that shows functional isomerism is **Part D** (CH3CH2CHO and CH3COCH3).