Question

which of thh following reactants would you add to an aqueous solution of ammonium sulfate in order to precipitate quantitatively all the sulfate?
A. CaCl2
b. Al(NO3)3
c. Zn(C2H3)2)2
d. KBr

Answer 1

So the question you are asking is this.
What are the solubilities of
CaSO4
Al2(SO4)3
ZnSO4
K2SO4.

Here is a simplified set of rules to help decide.
http://www.files.chem.vt.edu/RVGS/ACT/notes/solubility_rules.html

Answer 2

CaCl2

Answer 3

cacl2