An aqueous solution containing compounds A and B shows optical activity. A and B are stereoisomers. Which of the following
possibilities cannot be correct?

Options

A. A has two centers, but B does not have any because it
has a symmetry plane
B. A and B are enatiomers.
C. A and B are distereomers.
D. A and B are not present in equal amounts

Answer

To solve the question regarding the optical activity of compounds A and B, which are stereoisomers, we need to analyze the characteristics of stereoisomers and the implications of optical activity.

### Step-by-Step Solution:

1. **Understanding Optical Activity**:
- Optical activity refers to the ability of a compound to rotate plane-polarized light. For a compound to be optically active, it must lack a plane of symmetry and possess at least one chiral center (asymmetric carbon).

2. **Identifying Stereoisomers**:
- Stereoisomers are compounds that have the same molecular formula and connectivity of atoms but differ in the spatial arrangement of atoms. There are two main types of stereoisomers: enantiomers (which are non-superimposable mirror images) and diastereomers (which are not mirror images).

3. **Analyzing the Given Information**:
- We are told that both A and B are optically active and are stereoisomers. This indicates that both compounds must have chiral centers and cannot have a plane of symmetry.

4. **Evaluating the Possibilities**:
- **Possibility 1**: A has two chiral centers, but B has none due to symmetry.
- This cannot be correct because if A is optically active (having chiral centers), B cannot be optically inactive (having a plane of symmetry) if they are both present in the solution and are stereoisomers.
- **Possibility 2**: A and B are enantiomers.
- This can be correct as enantiomers are stereoisomers and both can be optically active.
- **Possibility 3**: A and B are diastereomers.
- This can also be correct since diastereomers can have different optical activities.
- **Possibility 4**: A and B are not present in equal amounts.
- This is possible as the optical activity does not require a racemic mixture; they can exist in unequal amounts.

5. **Conclusion**:
- The only possibility that cannot be correct is **Possibility 1**: A has two centers but B doesn't have any due to symmetry. This contradicts the condition that both A and B are optically active.

### Final Answer:
The possibility that cannot be correct is: **A has two centers but B doesn't have any because it has a symmetry.**