Verified answer

27,3 г                                                V=?

      2K       +    2H2O    =   2KOH  +   H2

 n=2 моль                                         n=1 моль

М= 39 г/моль                                   Vm=22,4 л/моль

m= 78 г                                              V=22,4 л

27,3 г К     -      Х л Н2

78 г К       -       22,4 л Н2

V(H2) = 27,3 * 22,4 / 78 = 7,84 л