Velocity is constant

In uniform flow, the velocity of the fluid remains constant at any given point in space and time. This means that the velocity does not change with respect to the X-axis. Hence, option 'A' - Velocity is constant - is the correct answer.

Explanation:

Uniform flow refers to the flow of a fluid where the velocity magnitude and direction remain constant at any given point in space and time. In other words, the fluid particles move parallel to each other in the same direction with the same velocity.

In the case of uniform flow parallel to the X-axis, the flow is in a straight line parallel to the X-axis. The fluid particles move in the same direction and with the same velocity along this line.

The X-component of velocity, which represents the velocity in the X-direction, remains constant in uniform flow parallel to the X-axis. This is because the flow is in a straight line parallel to the X-axis, and the fluid particles move only in this direction. Therefore, the X-component of velocity does not change.

On the other hand, the Y-component of velocity, which represents the velocity in the Y-direction perpendicular to the X-axis, is zero in uniform flow parallel to the X-axis. This is because the flow is constrained to only one direction, and there is no motion in the Y-direction.

Acceleration is also zero in uniform flow parallel to the X-axis. This is because acceleration is the rate of change of velocity, and since the velocity is constant, there is no change in velocity and therefore no acceleration.

Therefore, the correct answer is option 'A' - Velocity is constant - as the uniform flow parallel to the X-axis exhibits constant velocity.