How would I determine the relative acidity of substances?
In my homework one of the question was which of the following salt will produce a neutral solution(If any)? A) KI (Potassium Iodine) or B) SrS (Strontium Sulfur)

For (A) both K+ and I- will essentially stay as the ions. So assuming the solution is neutral to start, it will remain neutral.

But for (B), in a neutral solution, $\ce{Sr^{2+}}$ will stay as the ion,  $\ce{S^{2-}}$ will react as:

$\ce{S^{2-} + H2O &lt;=&gt; HS^- + OH-}$

so the solution will become slightly more basic. 

"Order the following from most acidic to least. $\ce{SO3}$, $\ce{CO3}$ and $\ce{CO2}$". 

I can't really make sense of this question since $\ce{CO3}$ is highly unstable, and there are three isomers. 

Bubbling  $\ce{SO3}$ and $\ce{CO2}$ gases into water would produce acidic solutioons via reactions

$\ce{SO3 + H2O -&gt; H2SO4}$

$\ce{CO2 + H2O -&gt; H2CO3}$