Which of the following statement/s is/are correct? I. Half-life is...

Which of the following statement/s is/are correct? I. Half-life is $50 \%$ of the total time taken for the completion of a reaction II. Collision frequency (Z), which is the number of collisions per second per unit volume, is same as the rate constant of the reaction III. A change in the activation energy of a reaction at a particular temperature will result in a proportional change in the rate and rate constant of the reaction at the same temperature IV. All first order reactions are not unimolecular V . For a zero order reaction, slope of a plot of $\mathrm{t}_{1/2} \mathrm{Vs}$. initial concentration will be zero