`KNO_3 + H_2 SO_4 ---gt KHSO_4 + HNO_3`
This is double displacement reaction. In this type of reaction, elements from two compounds displace each other to form new compounds i.e. one of the products exchange their ions and one of the products formed is insoluble.
In the given reaction, `K^+` ion in `KNO_3` and `H^+` ion in `H_2 SO_4`
displace each other and form `KHSO_4` and `HNO_3` .
Whereas in decomposition reaction a single compound breaks down into two or more simpler substances i.e. a compound decomposes into simpler substances.
An example for this decomposition reaction is
`CaCO_3 ----gt CaO + CO_2`
Calcium carbonate decomposes into quicklime (`CaO` ) and carbon dioxide (`CO_2` ).