Use the following answers for questions 1 - 3.

(A) F
(B) S
(C) Mg
(D) Ar
(E) Mn

3. Forms oxides that are common air pollutants and that yield acidic solution in water

I think the answer to this one is B, but why is it B? I see how it would yield an acidic solution, but what else would tell me that it is (B) S?

You are correct, S forms SO2 and SO3 and that added to water forms H2SO3 and/or H2SO4.
F forms no oxides.
Mg oxide adds to water to form a base, Mg(OH)2.
Ar is a noble gas and doesn't react with oxygen.
Mn forms an oxide but (a) isn't usually found in air as the metal (b) most of the oxides are not soluble in water.

So by the process of elimination, B is it and the SO2 and SO3 data confirms it.

Thank you very much!!