Answer:
Step-by-step explanation:
A compound must have a net charge of 0. The charges have to balance each other out and equal 0.
We have the compound sulfur trioxide with a chemical formula of SO₃.
Oxygen (O) has an oxidation state of -2, which means it will have a charge of -2 in the compound. However, note there is a subscript after the O in the chemical formula. Therefore, there are 3 oxygen atoms in the compound and each one has a charge of -2. The oxygen has an overall charge of -6 because 3*-2 = -6.
There is only one atom of sulfur (there is no subscript, so a 1 is implied). It has to balance out the -6 charge of the oxygen atoms, so it must be +6.
The oxidation number for sulfur is +6 in the compound sulfur trioxide.