массовая доля Na2SO4

 Mr(Na2SO4)= 23*2+32+16*4= 142

Mr (Na2SO4) = 23*2 + 32 + 64 = 142 г/мольw (Na) = 46/142*100% = 32,4%w (S) = 32/142*100% = 22,5%w (O) = 64/142*100% = 45,1%