Final answer:
Linear momentum is conserved in an elastic collision, where two objects collide and then separate with no loss of kinetic energy.
Step-by-step explanation:
The condition under which linear momentum is conserved is c. Elastic collision.
In an elastic collision, both linear momentum and kinetic energy are conserved. In this type of collision, two objects collide and then separate, with no loss of kinetic energy.
For example, when two billiard balls collide and then bounce off each other, the total momentum before the collision is equal to the total momentum after the collision.