Answer:
The answer to your question is the letter B.
Step-by-step explanation:
A double displacement reaction is a reaction in which the cation of a reactant displaces the cation of the other reactant and vice versa.
Examples of double-displacement reactions are Redox reactions or neutralization reactions.
Letter B is an example of a double displacement reaction because Barium displaces Hydrogen and vice versa. Also, this is a neutralization reaction because Ba(OH)₂ is a base and HClO₄ is an acid.