Assertion : Fibrins are formed by the conversion of inactive fibrinogens on the plasma by the enzyme thrombin
Reason : Plasma without fibrinogen and blood corpuscles is called serum.

Options

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

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin.
- This is true because fibrinogen, which is a soluble protein present in blood plasma, is converted into fibrin, an insoluble protein, during the blood clotting process. Thrombin acts as the enzyme that catalyzes this conversion.

2. **Understanding the Reason**:
- The reason states that plasma without fibrinogen and blood corpuscles is called serum.
- This is also true. Serum is the clear fluid that remains after blood has clotted and is devoid of fibrinogen and blood cells (like red blood cells and white blood cells).

3. **Analyzing the Relationship**:
- While both the assertion and the reason are true, the reason does not explain the assertion. The formation of fibrin from fibrinogen is a specific biochemical process related to blood clotting, while the definition of serum is a separate concept that describes the composition of blood after clotting.

4. **Conclusion**:
- Since both the assertion and the reason are true but the reason does not explain the assertion, the correct answer is that both are true, but the reason is not the correct explanation of the assertion.

### Final Answer:
The correct option is: **If both assertion and reason are true, but the reason is not the correct explanation of the assertion.**

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