Oxide of Sulphur means the compound formed is bonding between Sulphur and Oxygen.
Also, if the compound contains 60% Oxygen, then it must contain 40% Sulphur
Elements S O
%by mass of atoms 40 60
Divide by their masses 4032 6016
1.25 3.75
Divide through by smaller value 1.251.25 3.751.25
1 : 3
Empirical formula SO3
