What is the number of moles of H atoms required for complete reduction of one mole acetonitrile?

Reduction of acetonitrile follows the general catalytic hydrogenation reaction for nitriles: $R-C\equiv N + 2H_2 \xrightarrow{\text{catalyst}} R-CH_2NH_2$.

For acetonitrile ($CH_3CN$): $CH_3-C\equiv N + 2H_2 \rightarrow CH_3CH_2NH_2$.

Each mole of $H_2$ contains 2 moles of hydrogen atoms, so 2 moles of $H_2$ yield $2 \times 2 = 4$ moles of H atoms.

The complete reduction of one mole of acetonitrile requires 4 moles of H atoms.