Both statements I and II are individually true. When a gun is fired, it experiences a recoil, which means it pushes back with less velocity than the bullet. This is statement I.

Statement II states that the velocity of the recoiling gun is less because the gun is much heavier than the bullet. This is the correct explanation for statement I.

The recoil of the gun is a result of Newton`s third law of motion, which states that for every action, there is an equal and opposite reaction. When the bullet is fired from the gun, it creates a force in one direction, and the gun experiences an equal and opposite force in the other direction, causing it to recoil.

The velocity of the recoiling gun is less than the velocity of the bullet because the gun is much heavier. According to Newton`s second law of motion, the acceleration of an object is inversely proportional to its mass. Since the gun has a higher mass compared to the bullet, it experiences less acceleration, resulting in a lower velocity.

Therefore, option 1 is the correct answer as both statements are true, and statement II provides the correct explanation for statement I.