Assertion: Work done by the friction or viscous force on a moving body in negative.
Reason: Work done is a scalar quantity which cannot be negative like mass.

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

Explanation

To analyze the assertion and reason provided in the question, we will break down each statement step by step.

### Step 1: Understanding the Assertion
**Assertion:** Work done by the friction or viscous force on a moving body is negative.

- **Explanation:** When a body is moving, and there is a frictional force acting against its direction of motion, the work done by this frictional force is considered negative. This is because work done (W) is calculated using the formula:
\[ W = F \cdot d \cdot \cos(\theta) \]
where \(F\) is the force, \(d\) is the displacement, and \(\theta\) is the angle between the force and the displacement vector. In the case of friction, the angle \(\theta\) is 180 degrees (since friction acts opposite to the direction of motion), leading to:
\[ W = F \cdot d \cdot \cos(180^\circ) = -F \cdot d \]
Therefore, the assertion is **true**.

### Step 2: Understanding the Reason
**Reason:** Work done is a scalar quantity which cannot be negative like mass.

- **Explanation:** The statement that work done is a scalar quantity is correct; however, the assertion that it cannot be negative is incorrect. Work done can indeed be negative when the force acts in the opposite direction to the displacement (as shown in the previous step). Mass is also a scalar quantity, but it is always positive. Therefore, while the reason correctly identifies work as a scalar quantity, it incorrectly states that it cannot be negative. Thus, the reason is **false**.

### Conclusion
- **Assertion:** True (Work done by friction is negative)
- **Reason:** False (Work can be negative, unlike mass)

### Final Answer
The correct answer is that the assertion is true, but the reason is false.

---