Assertion: Diastereoisomers have different physical properties.
Reason: They are non-superimpossible mirror images.

Options

A. if both Assertion and Reason are true and reason is the correct explanation of the assertion.
B. if both assertion and reason are true but reason is not the correct expalanation of the assertion
C. if assertion is true, reason is false
D. both assertion and reason are false statements.

Explanation

To solve the given question, we need to analyze the assertion and the reason provided.

### Step 1: Understanding the Assertion
The assertion states that "Diastereoisomers have different physical properties."
- **Explanation**: Diastereoisomers are stereoisomers that are not related as mirror images. They can differ in various physical properties such as boiling points, melting points, and densities. This is a true statement.

### Step 2: Understanding the Reason
The reason states that "They are non-superimposable mirror images."
- **Explanation**: This statement is incorrect. Diastereoisomers are not mirror images of each other; that characteristic is true for enantiomers. Diastereoisomers are non-superimposable but not mirror images.

### Step 3: Conclusion
- Since the assertion is true and the reason is false, we conclude that the assertion is correct while the reason is incorrect.

### Final Answer
- The assertion is correct, and the reason is incorrect.