A : The area under acceleration - time graph is equal to velocity of object.
R : For an object moving with constant acceleration, position - time graph is a straight line.

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 analyze the given statements regarding motion in a straight line, we will break down the assertion (A) and the reason (R) step by step.

### Step 1: Understanding Assertion (A)
The assertion states that "The area under the acceleration-time graph is equal to the velocity of the object."

**Analysis:**
- The area under an acceleration-time graph represents the change in velocity of an object, not the absolute velocity. This is because acceleration is defined as the rate of change of velocity with respect to time (a = dv/dt).
- Therefore, when we calculate the area under the acceleration-time graph, we obtain the change in velocity (Δv = v_final - v_initial).

**Conclusion:**
- The assertion (A) is **incorrect** because it incorrectly states that the area under the graph equals the velocity instead of the change in velocity.

### Step 2: Understanding Reason (R)
The reason states that "For an object moving with constant acceleration, the position-time graph is a straight line."

**Analysis:**
- When an object moves with constant acceleration, the relationship between position (s), velocity (v), and time (t) can be described by the equations of motion.
- If acceleration is constant, the velocity changes linearly with time. The position, which is the integral of velocity, will be a quadratic function of time (s = (1/2)at² + v₀t + s₀), resulting in a parabolic graph rather than a straight line.
- Therefore, the statement that the position-time graph is a straight line is also **incorrect**.

### Conclusion
Both the assertion (A) and the reason (R) are incorrect.

### Final Answer
- Assertion (A) is **false**.
- Reason (R) is **false**.