Answer: Option (d) is the correct answer.
Step-by-step explanation:
A chemical reaction in which a compound dissociates to give two different compounds or atoms is known as a dissociation reaction.
For example,

Here, sulfurous acid dissociates into water and sulfur dioxide gas. Both water and sulphur dioxide have different properties than sulfurous acid.
Therefore, we can conclude that the given reaction is an example of a decomposition reaction.