A) When external forces are involved, momentum of the system is not conserved.
B) When stationary bomb explodes, energy released is converted to K.E of fragments
C) When rubber ball hits the wall, its kinetic energy is not conserved.

• A fundamental principle of physics known as the conservation of momentum holds that, in the absence of external forces acting on a system, its momentum will remain constant. The first law of Newton contains it (the law of inertia).
• KE of pieces are created from chemical energy.
  The kinetic energy was formerly zero, but now it is positive or zero for every little component, increasing the system's overall K.E.
• Rubber ball has a high degree of elasticity; as a result, when it strikes a wall, it is compressed but soon returns to its original shape thanks to elasticity. This causes it to push back against the wall. It therefore bounces back. A metal ball can be said to have zero velocity when it strikes a wall since the majority of its energy is transferred to the wall.

Hence the correct answer is A,B,C are true.