Masa molara Na₂SO₄=2*23+1*32+4*16=142
142g Na₂SO₄..............46g Na.............32g S............64g O
100g.............................x....................y...................z
x=46*100/142=32.39%Na
y=32*100/142=22.53%S
z=64*100/142=45.07%O
raspuns corect C)