Question

why are decomposition reaction called opposite of combination reaction write equation for this reaction ​

Answer 1

In a combination reaction two or more substances are combined to form new substance while in the decomposition reaction one substance decomposes into two or more substances. Hence, the decomposition reactions are called opposite of combination reactions.
this attachment is ur equation.

Answer 2

Because in combination reaction both reactant combines

together to give single substances or products but in decomposition reaction single product decomposes into two or three products