What is the oxidation number for S in the compound SO3? (Recall that O has an oxidation number of - 2.)

0

+2

+4

+6

Answer is: the oxidation number for S (sulfur) is + 6.

One molecule of sulfur trioxide (SO₃) has one sulfur atom and three oxygen atoms.

Sulfur trioxide (SO₃) has neutral charge:

x + 3 · (-2) = 0.

x = + 6; oxidation number of sulfur.

Oxygen has greater electronegativity than sulfur, so oxygen (shared electrons are closer to oxygen atom) has negative oxidation number.

Electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.