Ostwald's process is a chemical process for making nitric acid $\text{HNO}_3$ by which of the following methods:

Question

$\begin{array}{1 1}(a)\;Reduction\;of\;NH_3\\(b)\;Oxidation\;of\;NH_3\\(c)\;Hydrogenation\;of\;NH_3\\(d)\;Hydrolysis\;of\;NH_3\end{array}$