Both A and R are individually true and R is the correct explanation of A.

Explanation:

The assertion states that a chemical reaction becomes faster at higher temperatures, which is true. Increasing the temperature of a chemical system typically leads to an increase in the rate of reaction. This is due to the higher kinetic energy and increased molecular motion of the reactant molecules at higher temperatures.

The reason provided states that at higher temperatures, molecular motion becomes more rapid, which is also true. As the temperature rises, the average kinetic energy of molecules increases, causing them to move faster and collide more frequently. These more energetic collisions result in a greater number of effective collisions between reacting molecules, leading to an increase in the reaction rate.

Therefore, the reason (R) correctly explains why a chemical reaction becomes faster at higher temperatures, and both the assertion (A) and the reason (R) are true.