Common Ion Effect

The complex ion formed when the film developed in black and white photography is washed with hypo solution is

Explanation:

In black and white photography, hypo (sodium thiosulfate) solution is used to dissolve the silver halides remaining on the photographic film after exposure. When the film is washed with hypo solution, it forms a complex ion with silver ions, specifically , where thiosulfate ions act as ligands binding to silver ions.