Two reactants exchange component parts.

• A. Single displacement reactions
• B. Metathesis (displacement) reactions
• C. Oxidation-reduction reactions
• D. Precipitation reactions

Answer: (B)

The idea being tested is metathesis, or double displacement. In this type of reaction, ions from two reactants swap partners to form two new compounds, typically written as AB + CD → AD + CB. That is exactly what “exchange component parts” describes: each reactant contributes a part that ends up in a new compound, so the ions effectively trade places.

This isn’t about one element replacing another in a single compound, which would be single displacement, or about electron transfer and changing oxidation states, which is oxidation–reduction. It’s also not defined by whether a solid precipitate forms, since that can be a consequence of metathesis (a precipitate is simply one possible outcome). For example, NaCl reacting with AgNO3 yields NaNO3 and AgCl, illustrating ions swapping partners to give two new substances, with a solid possibly forming.