Question

when dissolved in an aqeous solution, which of the following salts will yield an acidic solution? NH4Cl, NaClO4, Na2S, MgBr2, Ba(CH3CO2)2

Answer 1

You look at the hydrolysis of each salt. For example, NH4Cl.
The Cl^- is a weak base and will not pull H^+ away from water; therefore, Cl^- is not hydrolyzed. The NH4^+ will donate a H^+ to water forming.
NH4^+ H2O ==> NH3 + H3O^+, thus, this is an acidic solution.
All of the texts and most teachers use this approach and if you are familiar with the acidity and/or basicity of catins and anions, this works quite well. However, WAY BACK when I was a student, we didn't use the Bronsted-Lowry theory that much so we had another way to do it. Your teacher won't like this, probably, but it works.
I write the molecular equation, for example, for NH4Cl.
NH4Cl + HOH ==> NH4OH + H^+
NH4OH (which has now been shown not to exist but it is NH3 + H2O) is a weak base, HCl is a strong acid, strong wins out over weak, so the salt is acidic in aqueous solution.
Another one.
NaClO4 + HOH ==> NaOH + HClO4.
NaOH is a strong base, HClO4 is a strong acid, the solution will be neutral.
Na2S + HOH ==> NaOH + H2S (not balanced), NaOH is a strong base, H2S is a weak acid, strong base wins out and the salt will be basic.
I hope this helps.