Match the metals/ions/compounds given in Column-I with the reactions where they act as catalyst as given in Column-II.
\[
\begin{array}{llll}
(a) & V_2O_5 & (p) & \text{Synthesis of ammonia by Haber's process} \\[6pt]
(b) & \text{Fe powder} & (q) & \text{Hydrogenation of alkene} \\[6pt]
(c) & Fe^{3+} & (r) & \text{Manufacture of } H_2SO_4 \text{ by Contact Process} \\[6pt]
(d) & \text{Ni(s)} & (s) & \text{Oxidation of } I^- \text{ by } S_2O_8^{2-}
\end{array}
\]