If a particle moving in a straight line, the following graph shows

The correct answer is Acceleration is constant.

Concept:

•  The rate of change of velocity of a body is called the acceleration of that body.
• It is a vector quantity that has both magnitudes as well as direction. 

\(acceleration\left( a \right) = \frac{{Change\;in\;velocity}}{{time\;taken}} = \frac{{{v_2} - {v_1}}}{{{t_2} - {t_1}}}or\frac{{dv}}{{dt}}\)

• The slope (m) of the displacement-time graph at any point will give the instantaneous velocity at that point.
• The slope of any graph at a point is given by: Slope (m) = tanθ
• Where θ is the angle made by the point with the x-axis.

Explanation:

• The given graph shows acceleration vs time graph
• In our case, the slope of the given graph is zero since the angle (θ) in our case is zero
• i.e., \(\tan \theta = \frac{{da}}{{dt}} \Rightarrow \frac{{da}}{{dt}} = 0\)
• From this we can see that rate of change of acceleration is zero hence the acceleration throughout the motion must remain constant.
• Hence option 2 is correct