Right choice is (a) Less than the kinetic energy of the bullet
For explanation: By conservation of momentum,
MV = mv or V = mv/M
Kinetic energy of the rifle is
Kr = 1/2MV^2 = 1/2M(m^2 v^2)/M^2
Kr = m/M * Kb
As m is lesser than M, Kr is lesser than Kb
Thus the kinetic energy is less than that of the bullet.