[A]: Kornberg and Ochoa got Nobel Prize in the field of genetics.
[R]: Because they proposed mutation Theory

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To solve the question regarding the assertion and reason provided, we will analyze both statements step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "Kornberg and Ochoa got the Nobel Prize in the field of genetics."
- We need to verify if this statement is true. Arthur Kornberg and Severo Ochoa were awarded the Nobel Prize in Physiology or Medicine in 1959 for their work on the mechanisms of RNA and DNA synthesis. Therefore, the assertion is **true**.

2. **Understanding the Reason**:
- The reason states that "they proposed mutation theory."
- We need to check the validity of this statement. The mutation theory was actually proposed by Hugo de Vries, not by Kornberg and Ochoa. Therefore, the reason is **false**.

3. **Evaluating the Relationship**:
- Now we need to determine the relationship between the assertion and the reason.
- The assertion is true, but the reason is false. Thus, the reason does not provide a correct explanation for the assertion.

4. **Conclusion**:
- Based on the evaluation, we can conclude that the correct answer is that the assertion is true and the reason is false.

### Final Answer:
The correct option is **third**: "Assertion is true and reason is false."

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