A threefold increase in the initial concentration of a leads to a ninefold increase in the initial rate. order with respect to a: a threefold increase in the initial concentration of a leads to a 1.73-fold increase in the initial rate. order with respect to a: a threefold increase in the initial concentration of a leads to a threefold increase in the initial rate. order with respect to a: a threefold increase in the initial concentration of a has no impact on the initial rate. order with respect to a?