The sum of the total number of neutrons present in protium,deuterium,and tritium is:

Which is the lightest gas?

State True or False for the following statements:
$1$. Metals of group $7$,$8$ and $9$ form non-stoichiometric hydrides.
$2$. Pure dihydrogen is obtained by heating hydrocarbons with $H_2O$ vapour in the presence of a $Ni$ catalyst at $1270 \ K$.
$3$. The ionization enthalpy of hydrogen is higher than that of alkali metals.
$4$. Some chemical properties of hydrogen resemble both metals and non-metals.

Hydrogen from $HCl$ can be prepared by

During the water-gas shift reaction:

Which statement is not correct for ortho and para hydrogen?