$Cu+H_2\quad\underrightarrow {heat}\quad Cu+x$,$ZnO+y\quad\underrightarrow{heat} \quad Zn+H_2O$,$2AgCl+H_2\rightarrow z+w$.The $x$ is

Question

$\begin{array}{1 1}(a)\;H_2\\(b)\;H_2O\\(c)\;2H_2O\\(d)\;2H_2\end{array}$