Assertion (A) is true: Reaction rates generally increase with temperature. This is a fundamental principle in chemical kinetics (Arrhenius equation). Reason (R) is true: At higher temperatures, molecules have higher kinetic energy and thus move more rapidly. The reason is a correct explanation for the assertion: Increased molecular motion at higher temperatures leads to more frequent collisions between reactant molecules and, more importantly, a higher proportion of these collisions having sufficient energy (activation energy) to overcome the energy barrier and result in a reaction.