M BaSO4= 137+ 32+ 4*16=233
233g BaSO4.................137g Ba.............32gS.................64gO
100g BaSO4..................x g Ba.............y gS..................z g O
x= 100*137 / 233=58,79% Ba
y=100*32 / 233=13,73%S
z= 100*64 / 233=27,46% O
58,79% Ba, 13,73% S si 27,46% O