To free the electron from metal surface minimum energy required, is equal to the work function of that metal. So Assertion A, is correct. hv=w0+K.E⋅max if hv=w0 ⇒K⋅⋅max=0 Hence reason R, is correct, But R is not the correct explanation of A. When energy of incident radiation is equal to the work function of the metal, then the KE of photoelectrons would be zero. But this statement does not comment on the situation when energy is less than the work function.