$H_2$ gas can be prepared by 

Electrolysis of  Acidulated water:

(A) At Anode: Oxidation reaction$2\overline{OH}\to H_{2}O+\frac{1}{2}{O}_2+2\overline{e}$

At cathode: Reduction reaction  $2H_{2}O+2\overline{e}\to 2\overline{OH}+H_2$

Over all reaction = $H_{2}O\to H_2\uparrow \frac{1}{2}{O}_2$

(B)  $Mg+H_{2}S{O}_4\to MgS{O}_4+H_2\uparrow$

(C) $2Al+2NaOH+2H_{2}O\to 2NaAl{O}_2+3H_2$

(D) $\underset{Coke}{C+H_2}O\stackrel{1000ºC}{\to }{\underset{Stream}{CO+H}}_2\uparrow$