Why does hydrogen occur in a diatomic form rather than in a monoatomic form under normal conditions?

Among the following,the correct statement is

Name the classes of hydrides to which $H_2O$,$B_2H_6$ and $NaH$ belong.

On passing electric current over molten ionic hydrides of $s-$block elements,

Which of the following statements are $NOT$ correct?
$A$. Hydrogen is used to reduce heavy metal oxides to metals.
$B$. Heavy water is used to study reaction mechanism.
$C$. Hydrogen is used to make saturated fats from oils.
$D$. The $H-H$ bond dissociation enthalpy is lowest as compared to a single bond between two atoms of any elements.
$E$. Hydrogen reduces oxides of metals that are more active than iron.
Choose the most appropriate answer from the options given below:

Which of the following will not be reduced by $H_2$?