There is a colour change observed in silver bromide when exposed to sunlight. This is due to

The correct option is C.

photochemical decomposition

When silver bromide is exposed to sunlight, decomposition reaction takes place, which results in the formation of silver and bromide gas. This decomposition reaction is also called photochemical reactions, where white AgBr converts into grey colour silver in the presence of light.

$2AgBr\to 2Ag+B{r}_2$

A combination reaction would require combination of reactants to make a product, the converse is happening above.

There is no displacement of elements in above mentioned reaction, so it cannot be a displacement reaction.