A. The successive half lives of zero order reactions decreases with time. This statement is correct. The half-life of a zero-order reaction is given by the formula $t_{1/2} = [A]_0/2k$, where $[A]_0$ is the initial concentration and k is the rate constant. As the concentration decreases, the half-life also decreases.

B. A substance appearing as reactant in the chemical equation may not affect the rate of reaction. This statement is correct. For example, in a zero-order reaction, the rate of reaction does not depend on the concentration of reactants.

C. Order and molecularity of a chemical reaction can be a fractional number. This statement is incorrect. The order of a reaction can be zero, fractional or negative. However, molecularity, which refers to the number of reactant molecules taking part in an elementary reaction, can only be a whole number.

D. The rate constant units of zero and second order reaction are

and respectively. This statement is correct. The units of the rate constant for a zero-order reaction are M/s or mol·L⁻¹·s⁻¹ . The units of the rate constant for a second-order reaction are 1/(M·s) or L·mol⁻¹·s⁻¹ .