What is limiting reactant?

(i) What is limiting reactant ?
(ii) Oxygen is prepared by catalytic decomposition of potassium chlorate (KCl${{O}{3}}$). Decomposition of potassium chlorate gives potassium chloride (KCl) and oxygen (${{O}{2}}$). If 2.45 mol of oxygen is needed for an experiment, how many grams of potassium chlorate must be decomposed ?