A : In the presence of air resistance, if the ball is thrown vertically upwards then time of ascent is less than the time of descent.
R : Force due to air friction always acts opposite to the motion of the body.

Options

A. If both Assertion & Reason are true and the reason is the correct explanation of the assertion, then mark (1).
B. If both Assertion & Reason are true but the reason is not the correct explanation of the assertion, then mark (2).
C. If Assertion is true statement but Reason is false, then mark (3).
D. If both Assertion and Reason are false statement, then mark (4).

Answer

To solve the question, we need to analyze the assertion and reasoning provided:

**Assertion (A):** In the presence of air resistance, if the ball is thrown vertically upwards, then the time of ascent is less than the time of descent.

**Reason (R):** Force due to air friction always acts opposite to the motion of the body.

### Step-by-Step Solution:

1. **Understanding the Motion of the Ball:**
- When a ball is thrown vertically upwards, it moves against the force of gravity (g) and also experiences air resistance (drag force).
- During the ascent, both the gravitational force and the drag force act downward.

2. **Analyzing Forces During Ascent:**
- The net force acting on the ball during ascent is:
\[ F_{\text{net, ascent}} = -mg - F_{\text{drag}} \]
- This results in a greater effective acceleration acting downwards, which means the ball will decelerate more quickly than it would without air resistance.

3. **Understanding Time of Ascent:**
- Because the ball experiences a greater effective downward acceleration, it will take less time to reach its maximum height compared to a scenario without air resistance.

4. **Analyzing Forces During Descent:**
- When the ball starts descending, the forces acting on it are gravity (downward) and air resistance (upward).
- The net force during descent is:
\[ F_{\text{net, descent}} = mg - F_{\text{drag}} \]
- Here, the effective acceleration downward is reduced due to the opposing drag force.

5. **Understanding Time of Descent:**
- Since the effective acceleration during descent is less than during ascent, the ball will take more time to fall back to the ground.

6. **Conclusion:**
- Therefore, the assertion that the time of ascent is less than the time of descent is correct.
- The reason provided is also valid as it explains why the forces act in opposite directions during ascent and descent.

### Final Answer:
Both the assertion (A) and the reason (R) are correct, and the reason correctly explains the assertion.