Question

how does increasing reactants concentrations increase the rate of a reaction?
increasing the frequency of collisions
increasing the frequency of collisions and the proportion of molecules with sufficient energy, the $e_a$
lowering the $e_a$
lowering the $delta h$

Explanation:

Increasing reactant concentrations means more reactant particles in a given volume. This leads to a higher frequency of collisions between particles, which is necessary for a reaction to occur. Changing reactant concentration does not affect the proportion of molecules with sufficient energy (activation energy $E_a$) or $E_a$ itself or $\Delta H$.

Answer:

Increasing the frequency of collisions