The kinetic theory assumes that collisions of gas particles are perfectly elastic. what does this statement mean?

Imagine that you have two molecules flowing in a space in a straight line. with pure coincidence, the two molecules collide with each other. when the collide, they bounce off each other with no loss in speed. This collision is elastic because there is no loss of speed and energy. This type of collision is not very common, with few example in gas particles.

Rate law for this reaction israte of the reaction = k[a]²[b].second order in a  means concentration of a in power of two, and  first order in b means concentration of b in power of one.