Assertion : Force is defined as a push or a pull acting on a body.
Reason : CGS unit of force is newton

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 assertion is false but reason is true.

Explanation

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

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states, "Force is defined as a push or a pull acting on a body."
- This definition is correct. Force is indeed described as a push or pull that can cause an object to move or change its motion.

2. **Understanding the Reason**:
- The reason states, "CGS unit of force is newton."
- This statement is incorrect. The CGS (Centimeter-Gram-Second) system uses the unit "dyne" for force, not "newton." The newton is the SI (International System of Units) unit of force.

3. **Evaluating the Truth of Each Statement**:
- Since the assertion is true and the reason is false, we can summarize:
- Assertion: True
- Reason: False

4. **Choosing the Correct Option**:
- The options provided are:
1. Both assertion and reason are true, and reason is the correct explanation of assertion.
2. Both assertion and reason are true, but reason is not the correct explanation of assertion.
3. Assertion is true, and reason is false.
4. Assertion is false, and reason is true.
- Based on our evaluation, the correct choice is option 3: "Assertion is true, and reason is false."

### Final Answer:
The correct option is **Option 3**: Assertion is true, and reason is false.