Question

why do we store silver chloride in dark coloured bottles explain in brief

Answer 1

This prevents the breakdown of silver chloride into its elements.

When silver chloride is hit with light, it breaks down into elemental silver and chlorine gas:

2AgCl→2Ag+Cl2       the amount of chlorine gas formed in the reaction is generally small enough so there's no danger. However, during this process the silver chloride itself is contaminated with silver, which darkens its colour