2,4 г                                                                  Х л

    Mg          +         2HCl      =      MgCl2      +      H2

n = 1 моль                                                          n = 1 моль

Mr = 24 г/моль                                                   Vm = 22,4 л/моль

m = 24 г                                                              V = 22,4 л

2,4 г Mg    -    Х л Н2

24 г Mg    -    22,4 л Н2

V(H2) = 2,4 * 22,4 / 24 = 2,24 л