31,5 г                                        Х г

   HNO3        +        KOH      =     KNO3      +       H2O

n = 1 моль                                 n = 1 моль

Mr = 63 г/моль                          Mr = 101 г/моль

m = 63 г                                     m = 101 г

31,5 г HNO3     -    Х г KNO3

63 г HNO3        -    101 г KNO3

m(KNO3) = 31,5 * 101 /63 = 50,5 г