In what type of reaction, white coloured AgCl₂ is turned grey in colour?

You will see that white silver chloride turns grey in sunlight. This is due to the decomposition of silver chloride into silver and chlorine by light.

2AgCl(s) ­­­à 2Ag(s) + Cl₂(g)

When white silver chloride (AgCl) is exposed to sunlight, it undergoes a chemical reaction that causes it to turn grey. This change happens due to the decomposition of silver chloride into its constituent elements, silver (Ag) and chlorine (Cl), under the influence of light. The process is a type of photochemical reaction, where the energy from the sunlight provides enough energy to break the bonds in silver chloride. The silver ions are reduced to metallic silver, which gives the substance its grey color, while chlorine gas is released.

This reaction is a classic example of how light can drive chemical changes. The decomposition of silver chloride is not just a visual change but also a demonstration of the broader concept of photochemical reactions, where light energy can break chemical bonds and cause substances to change their chemical structure.