Răspuns:
MP2O5=2AP+5AO=2×31+5×16=62+80=142g/mol
MMgO=AMg+AO=24+16=40g/mol
MNa2SO4=2ANa+AS+4AO=2×23+32+4×16=46+32+64=142g/mol
MNaOH=ANa+AO+AH=23+16+1=40g/mol
Perechi:a - c și b - d
