Question

How photochemical reaction played an important role in the photography

Answer 1

Photography involves a photochemical process which converts silver bromide to metallic silver by the action of photochemical reaction. 
2 AgBr ----> 2 Ag + Br2 
Silver bromide is used as an emulsion which develops a photographic image. On exposure to light silver bromide is decomposed to metallic silver and it preserves the photographic image. 

Answer 2

Answer:

Photographic film is used in black and white photography is celluloid film coated with silver chloride

Explanation:

It's working is based on decomposition of silver chloride in presence of sunlight

2AgCl--------- 2Ag+Cl2