In S.H.M. at the equilibrium position    a) Amplitude is minimum    b) Acceleration is zero          c) Velocity is maximum   d) P.E is maximum

Amplitude is the maximum distance of a particle from equilibrium position during the course of oscillation. So (a) is wrong as amplitude remains constant. Acceleration . At equilibrium x = 0, so (b) is right . At equilibrium, x = 0 So (c) is right. At equilibrium, x = 0 so U = 0. Therefore (d) is wrong.