The balanced chemical equation for the reaction between silver nitrate and aluminum sulfate is:
$$3AgNO_3(aq) + Al_2(SO_4)_3(aq) → 3Ag_2SO_4(s) + 2Al(NO_3)_3(aq)$$
In this reaction, the silver ions (Ag+) from silver nitrate exchange with the aluminum ions (Al3+) from aluminum sulfate, and the nitrate ions (NO3-) from silver nitrate exchange with the sulfate ions (SO42-) from aluminum sulfate. The products of the reaction are silver sulfate, which is a precipitate (a solid that forms when two solutions are mixed), and aluminum nitrate, which is soluble in water.
The net ionic equation for the reaction is:
$$2Ag^+ + SO_4^{2-} → Ag_2SO_4(s)$$
This equation shows that the actual reaction that occurs is between silver ions (Ag+) and sulfate ions (SO42-).