Which element forms the maximum number of compounds in chemistry?

When steam is passed over red hot iron,the substances formed are

Hydrogen readily combines with metals and thus shows its

Complete the following reactions:
$(i)$ $H_{2(g)} + M_mO_{o(s)} \xrightarrow{\Delta} M_{(s)} + H_2O_{(l)}$
$(ii)$ $CO_{(g)} + 2H_{2(g)} \xrightarrow{\Delta, \text{ catalyst}} CH_3OH_{(l)}$
$(iii)$ $C_3H_{8(g)} + 3H_2O_{(g)} \xrightarrow{\Delta, \text{ catalyst}} 3CO_{(g)} + 7H_{2(g)}$
$(iv)$ $Zn_{(s)} + 2NaOH_{(aq)} \xrightarrow{\text{heat}} Na_2ZnO_{2(aq)} + H_{2(g)}$

Very pure hydrogen $(99.9 \%)$ can be made by which of the following processes?

Saline hydrides are known to react with water violently producing fire. Can $CO_2$,a well-known fire extinguisher,be used in this case? Explain.