Presence of chiral center is not an essential condition to show optical isomerism. Essential condition is, compound should show non-superimposable mirror image.
Allenes do not contain chiral center but show optical isomerism when different groups are attached on double bonded carbons.
Biphenyls also show optical isomerism when both rings are perpendicular to each other and any ring should not contain plane of symmetry.
Which of the following compounds is optically inactive?

Options

A.
B.
C.
D.

Explanation

To determine which of the following compounds is optically inactive, we need to analyze the provided information about optical isomerism and the conditions under which a compound is considered optically active or inactive.

### Step-by-Step Solution:

1. **Understand Optical Isomerism**:
- Optical isomerism occurs when a compound can exist in two forms that are non-superimposable mirror images of each other. This typically requires the presence of a chiral center, but as stated, it is not an essential condition.

2. **Identify Chiral Centers**:
- A chiral center is usually a carbon atom bonded to four different groups. If a compound lacks a chiral center or has a plane of symmetry, it may be optically inactive.

3. **Analyze the Given Compounds**:
- We need to evaluate each compound based on the presence of chiral centers and the ability to form non-superimposable mirror images.

4. **Evaluate Each Option**:
- **Option 1**: If the compound has two identical groups attached to a carbon, it cannot be chiral and is likely optically inactive.
- **Option 2**: If the compound has different groups attached to the chiral center, it is likely optically active.
- **Option 3**: Similar to Option 2, if there are different groups around the chiral center, it is likely optically active.
- **Option 4**: If the compound is an allene with different substituents, it can show optical isomerism and is likely optically active.

5. **Conclusion**:
- After analyzing the compounds, we conclude that **Option 1** is the optically inactive compound because it has identical groups attached to a carbon, making it achiral.

### Final Answer:
The optically inactive compound is **Option 1**.