Metals of groups $7$,$8$,and $9$ do not form metallic hydrides. This is termed as

Which set of elements forms stable,covalent,and hydrogen-bonded hydrides?

Formic acid is heated with conc. $H_2SO_4$ at $100^{\circ}C$ to form $A$ and $B$. When $Fe_2O_3$ is heated strongly with $B$,the products formed are $C$ and $D$. $C$ can also be obtained by reacting $CaCO_3$ with dil. $HCl$. What is $D$?

Observe the following reactions:
$I$. $CO_{(g)} + H_{2(g)} \xrightarrow{X} HCHO_{(g)}$
$II$. $CO_{(g)} + 3 H_{2(g)} \xrightarrow{Y} CH_{4(g)} + H_2O_{(g)}$
The catalysts $X$ and $Y$ in the above reactions are respectively:

Which of the following metals absorbs hydrogen?

Identify the catalyst used in the following reaction: $CO_{(g)} + H_2O_{(g)} \xrightarrow{623 \ K} CO_{2_{(g)}} + H_{2_{(g)}}$