The one that will show optical activity is: (en = ethane-1,2-diamine)

Options

A.
B.
C.
D.

Explanation

To determine which compound shows optical activity, we need to analyze the given options for the presence of a plane of symmetry (POS). A compound is optically active if it does not possess a plane of symmetry.

### Step-by-Step Solution:

1. **Understanding Optical Activity**:
- Optical activity refers to the ability of a compound to rotate plane-polarized light. This property is typically exhibited by chiral molecules, which lack an internal plane of symmetry.

2. **Identifying the Compounds**:
- We have four compounds to analyze. The question specifies that "En" refers to ethane-1,2-diamine.

3. **Analyzing Each Compound**:
- **Option 1**: Check for a plane of symmetry. If a plane can be drawn that divides the molecule into two mirror-image halves, the compound is optically inactive.
- **Option 2**: Similarly, analyze this compound for symmetry. If it has a plane of symmetry, it is also optically inactive.
- **Option 3**: Again, check for a plane of symmetry. If it can be divided into two symmetrical halves, it is optically inactive.
- **Option 4**: This is the last compound to analyze. If no plane of symmetry can be drawn, then this compound is likely optically active.

4. **Conclusion**:
- After analyzing all options, we find that the last compound (Option 4) does not possess a plane of symmetry, indicating that it is optically active.

5. **Final Answer**:
- The compound that shows optical activity is **Option 4**.