Assertion(A): The zero velocity of a particle at any instant always implies zero acceleration at that instant 

Reason(R): A body is momentarily at rest when it reverses its direction of motion. 

The correct option among the following is 

Assertion(A): is false, because if we take the example of a ball thrown vertically upwards, then at the topmost point of its motion the ball momentarily comes to rest but acceleration due to gravity keeps on acting on the ball.

Reason: is true whenever any object reverses its direction of motion then the sign of velocity changes because it comes to rest for a moment at the point where it changes its direction of motion. The same example of motion of ball given above can be used to explain it as the ball changes the direction of motion after reaching the topmost point when its speed becomes zero for a moment