The correct option is C 10−3 M NH4OH
AgBr will have maximum solubility in 10−3M NH4OH.
Adding a common ion decreases solubility, as the reaction shifts towards the left to relieve the stress of the excess product.
In NH4OH, due to the formation of a coordination complex AgBr is more soluble.
AgBr→Ag++Br−NH3−−−→[Ag(NH3)2]Br