Four reactions are given below. Which one of them is of zero order? (a) PCl PCl Cl -> (b) 2FeCl SnCl 2FeCl SnCl -> (c) H Cl 2HCl -> (d) N O 2NO O -> Ans. (c) Sol. The order of all photochemical reactions is zero as it does not depend upon the concentration of reactants. So, H Cl 2HCl -> is a zero order reaction.