Развернуто , придирчивая учитель.​

2Na + H2SO4 = Na2SO4 + H2↑
2Na⁺ + 2H⁺+SO4²⁻=2Na⁺+SO4²⁻+H2↑
2H=H2↑
2Na+2HCl = 2NaCl + H2↑
2Na+2H⁺+2Cl⁻=2Na⁺+2Cl⁻+H2↑
2H⁺=H2↑
CaO + H₂SO₄=CaSO₄↓+H₂O
CaO+2H⁺+SO₄²⁻=CaSO₄↓+H₂O
CaO+2HCl = CaCl2+H2O
CaO +2H⁺+2Cl⁻=Ca²⁺+2Cl⁻+H2O
CaO+2H⁺ =Ca²⁺+H2O
Cu(OH)2+2HCl=CuCl2+2H2O
Cu(OH)2+2H+2Cl = Cu+2Cl+2H2O
Cu(OH)2+2H⁺ = Cu²⁻ + 2H2O
Na2CO3+H2SO4=Na2SO4+H2O+CO2
2Na⁺+CO3²⁻+2H⁺+SO4²⁻=2Na⁺+SO4²⁻+H2O+CO2
CO3²⁻+2H⁺=H2O+CO2
Na2CO3+2HCl=2NaCl+H2O+CO2
2Na⁺+CO3²⁻+2H⁺+2Cl⁻=2Na⁺+2Cl⁻+H2O+CO2
CO3²⁻+2H⁺=H2O+CO2
2Al+3H2SO4=Al2(SO4)3+3H2↑
2Al +6H⁺ +3SO4²⁻=2Al³⁺+3SO4²⁻+3H2↑
6H=3H2↑
2Al+6HCl = 2AlCl3+3H2↑
2Al+6H+6Cl=2Al+2Cl3+3H2↑
6H=3H2↑

     4 г                                                  Х г                   Х г

    2NaOH         +        H2SO4    =     Na2SO4     +    2H2O

n = 2 моль                                    n = 1 моль              n = 2 моль

Mr = 40 г/моль                            Mr = 142 г/моль       Mr = 18 г/моль

m = 80 г                                       m = 142 г                 m = 36 г

4 г NaOH   -    Х г Na2SO4

80 г NaOH   -   142 г Na2SO4

m(Na2SO4) = 4 * 142 / 80 = 7,1 г

4 г NaOH    -    Х г Н2О

80 г NaOH  -  36 г Н2О

m(H2O) = 4 * 36 / 80 = 1,8 г