Which of the following is the most abundant element in the universe?

The number of neutrons in tritium is

Given below are two statements :
Statement-$I$: Methane and steam passed over a heated $Ni$ catalyst produces hydrogen gas.
Statement-$II$: Sodium nitrite reacts with $NH_4Cl$ to give $H_2O$,$N_2$ and $NaCl$.
In the light of the above statements,choose the most appropriate answer from the options given below :

The single largest industrial application of dihydrogen is:

Give the uses of $Dihydrogen$.

$A$ deuteron contains