Mg + 2 HCl => MgCl2 + H2
m Mg = 4.8 g
M Mg = 24.3 g/mol
n = m/M => n Mg = 4.8 / 24.3 = 0.2 mol Mg
1 mol Mg ... 2 mol HCl ... 1 mol H2
0.2 mol Mg ...x mol HCl ...y mol H2
x=0.2 * 2 / 1= 0.4 mol HCl
y=0.2 *1 / 1 = 0.2 mol H2
V = n * 22.4 L/mol
V H2 = n H2 * 22.4 L/mol = 0.2 * 22.4 = 4.48 L H2 cn