An electrolytic cell is constructed for preparing hydrogen. For an average current of 1 ampere in the circuit, the time required to produce 450 mL of hydrogen at NTP is approximately. 

22,400 ml ${\mathrm{H}}_2$ at STP = 1 mol ${\mathrm{H}}_2$

$\therefore 450\text{\hspace{0.17em}mL\hspace{0.17em}}{\mathrm{H}}_2\text{ at STP =}\frac{450\text{ mL}}{22,400\text{ mL}}\times 1\text{ mole\hspace{0.17em}}{\mathrm{H}}_2$

$=0.02 \mathrm{mol}$

Electrode reaction: 

$2{\mathrm{H}}^{+}+2{\mathrm{e}}^{-}\to {\mathrm{H}}_2$

2 F                       1 mol

So, the liberation of 0.02 mole of ${\mathrm{H}}_2$ requires 

$=2\times 96,500\times 0.02\mathrm{C}=3860\mathrm{C}$

Time required to produce 0.02 mole 

$\mathrm{t} =\frac{\mathrm{Q}}{\mathrm{I}}=\frac{3,860}{1}=1.07\mathrm{\hspace{0.17em}}\mathrm{h}\approx 1 \mathrm{hour}$