how do the linear momentum and kinetic energy of the two-atom system after the collision compare to these quantities before the collision g

Explanation:

Two atoms with equal masses, m, and equal speed, v, engage in a head on elastic collision. Since, the two atoms both having equal masses and equal but opposite velocity, the total linear momentum of the system is zero. Therefore, conservation of linear momentum to be conserved , the velocities before and after collision are same. Similarly, in elastic collision total kinetic energy is also conserved. The kinetic energy before and after collision are same.

it is called kinetic energy