B

Inelastic Collision: In an inelastic collision, the two objects collide and move together as one mass after the collision. This type of collision typically occurs when the kinetic energy is not conserved, but momentum is conserved.

Step 1: Conservation of Momentum: In any collision (elastic or inelastic), momentum is always conserved. This means that the total momentum before the collision is equal to the total momentum after the collision.

Step 2: Kinetic Energy in Inelastic Collision: Unlike momentum, kinetic energy is not conserved in an inelastic collision. Some of the kinetic energy is transformed into other forms of energy (like heat or sound) during the collision.

Therefore, in an inelastic collision, momentum is conserved while kinetic energy is not. Hence, the correct answer is: Option B: Momentum.