Agcl is less soluble in nacl(aq) than in water because

1)of a decrease in na+ ions.

2)agcl forms complex ions with nacl.

3)of a common ion effect.

4)nacl has a higher solubility product

The reduction is solubility is because 3) of a common ion effect.
The common ion effect is when an ion that is already present in a solution is added, causing the following equilibrium to be disturbed:
AB ↔ [A+] + [B-]

If [B-] is added, then according to Le Chatelier's principle, the equilibrium must shift backward, creating more undissolved precipitate.