Why do internal forces acting within a system not affect its motion?

When a bomb explodes during projectile motion,which forces do not contribute to the motion of the centre of mass?

Choose the correct statement$(s)$:
$(A)$ The position of the centre of mass of a system is dependent on the choice of coordinate system.
$(B)$ Newton's second law of motion is applicable to the centre of mass of the system.
$(C)$ Internal forces cannot change the state of the centre of mass.
$(D)$ Internal forces can change the state of the centre of mass.

The multiplication of the total mass of a system and the acceleration of its centre of mass denotes what?

Why are the internal forces acting on the centre of mass of a system neglected?

If a force $10 \hat{i} + 15 \hat{j} + 25 \hat{k}$ acts on a system and gives an acceleration $2 \hat{i} + 3 \hat{j} - 5 \hat{k}$ to the centre of mass of the system,the mass of the system is