If a particle is moving on a circular path with constant speed, then the angle between the direction of acceleration and its position vector w.r.t centre of circle will be

dear Aryam, read the question carefully its CIRCULAR MOTION. 
 

Dear student, Since,v=dr/dt and also we know that in uniform Circular motion velocity vector is tangential (π) to the centripetal acceleration throughout the Circular motion .So,likewise position vector(r) will also be tangential (π) w.r.t. centre of the circle .

it answer is pi

Equal to pie

answer :  pi