Question

how to identify double displacement reaction?​

Answer 1

The easiest way to identify a double displacement reaction is to check to see whether or not the cations exchanged anions with each other.

Another clue: if the states of matter are cited, is to look for aqueous reactants and the formation of one solid product (since the reaction typically generates a precipitate).

Answer 2

Whenever you see any exchange of ions taking place as well as formation of a precipitate
You can observe a double displacement reaction


Bacl2 + Na2So4 gives rise to Nacl + BaSo4


Here the precipitate formed is BaSo4 in the solution of Nacl