A shell in flight explodes into n equal fragments. K of the fragments reach the ground earlier than the other fragments. The acceleration of their centre of mass subsequently will be

Question

$$\begin {array} {1 1} (a)\;g & \quad (b)\;(n-k)g \\ (c)\;\frac{(n-k)g}{k} & \quad  (d)\;\frac{(n-k)g}{n} \end {array}$$