This section contains Assertion (A) and Reason (R) type questions. Each question has choices (1), (2), (3) and (4), out of which only one is correct.
Assertion (A) During fertilisation only head of spermatozoa enters the egg.
Reason (R) If several spermatozoa hit the egg at same time, all can enter.

Options

A. Both Assertion and reason are correct, and Reason is the correct explanation of Assertion.
B. Both Assertion and Reason are correct, but Reason is not the correct explanation of Assertion.
C. Assertion is correct, but Reason is incorrect
D. Assertion is incorrect, but Reason is correct

Answer

To solve the assertion and reason question, we will analyze both the assertion and the reason separately and determine their correctness.

### Step-by-Step Solution:

1. **Understand the Assertion (A)**:
- The assertion states: "During fertilization, only the head of spermatozoa enters the egg."
- This is true. During fertilization, the head of the sperm, which contains the genetic material and the acrosome (which releases enzymes), penetrates the egg. The tail does not enter the egg.

2. **Understand the Reason (R)**:
- The reason states: "If several spermatozoa hit the egg at the same time, all can enter."
- This statement is false. In reality, when multiple spermatozoa reach the egg, only one sperm can successfully penetrate and fertilize the egg. The acrosome reaction triggered by the first sperm that penetrates the egg changes the egg's membrane, preventing other sperm from entering.

3. **Evaluate the Relationship**:
- The assertion is correct, but the reason is incorrect. The reason does not explain the assertion because it contradicts the biological mechanism of fertilization.

4. **Select the Correct Option**:
- Based on the analysis, the correct option is: "Assertion is correct but reason is incorrect." This corresponds to option (3).

### Final Answer:
The correct option is (3): Assertion is correct but reason is incorrect.