Consider the reactions:
$I$. $CO + 3 H_2 \xrightarrow{A} CH_4 + H_2 O$
$II$. $CO + 2 H_2 \xrightarrow{B} CH_3 OH$
$III$. $O_2 + 2 H_2 \xrightarrow{C} 2 H_2 O$
The catalysts $A, B, C$ are respectively:

Arrange the following:
$(i)$ $CaH_2$,$BeH_2$ and $TiH_2$ in order of increasing electrical conductance.
$(ii)$ $LiH$,$NaH$ and $CsH$ in order of increasing ionic character.
$(iii)$ $H-H$,$D-D$ and $F-F$ in order of increasing bond dissociation enthalpy.
$(iv)$ $NaH$,$MgH_2$ and $H_2O$ in order of increasing reducing property.

$N_2H_4$ and $H_2O_2$ show similarity in

The natural relative abundance of isotopes of hydrogen is:

Which of the following processes produces hydrogen with the highest purity $(99.9\%)$?

The element used for welding metals with high melting points is: