The rate of a reaction depends on how many effective collisions occur per unit time, and increasing reactant concentration packs more molecules into the same volume. With more molecules present, the number of collisions per second rises proportionally, so the frequency of effective collisions also increases and the reaction goes faster. This is the molecular basis of why rate laws contain concentration terms. The option that concentration lowers activation energy is incorrect, because activation energy is fixed for a given pathway and is only altered by a catalyst. The option that concentration raises temperature confuses two independent variables. The option that concentration changes the reaction order is wrong, since order is a fixed experimental property and concentration changes only the rate, not the order. This collision-frequency explanation links the macroscopic rate law to molecular behaviour in NCERT. Plausibility check: doubling concentration in a first order reaction doubles the rate, exactly matching a doubling of collision frequency, confirming the chosen answer.