SELF-PRACTICE — the source book printed no answer.
Nothing is invented here, so this question has no answer on record.
Explanation
(A) Ni present in coenzyme $\mathrm{F_{430}}$ (III) which catalyzes the release of methane (Y) in the final step of methanogenesis.(B) Zn present in carbonic anhydrase (I) which catalyses the hydration of $\mathrm{CO_2}$ into $\mathrm{H_2CO_3}$ (Z).(C) Mo present in Xanthine oxidase (II) which catalyzes the oxidation of Xanthine to uric acid (X).