Assertion : Acetylcholine participates in the nerve impulse transmission across a synapse.
Reason : Acetylcholine is secreted by adrenergic fibres.

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding the Assertion**: The assertion states that "Acetylcholine participates in the nerve impulse transmission across a synapse." This is true because acetylcholine is a key neurotransmitter that facilitates communication between nerve cells by transmitting signals across the synaptic gap.

2. **Understanding the Reason**: The reason states that "Acetylcholine is secreted by adrenergic fibers." This statement is false. Acetylcholine is primarily secreted by cholinergic fibers, not adrenergic fibers. Adrenergic fibers release norepinephrine, which is different from acetylcholine.

3. **Evaluating the Relationship**: Since the assertion is true and the reason is false, the reason does not provide a correct explanation for the assertion.

4. **Choosing the Correct Option**: Based on the evaluation:
- Option 1: Both assertion and reason are true, and reason is the correct explanation of assertion. (Incorrect)
- Option 2: Both assertion and reason are true. Reason is not the correct explanation of assertion. (Incorrect)
- Option 3: Assertion is true, but reason is false. (Correct)
- Option 4: Assertion is false, reason is true. (Incorrect)

Thus, the correct answer is Option 3: Assertion is true, but reason is false.

---