Which statement describes a double replacement reaction?

• A. A selection of elements rearranges to form new compounds
• B. Two elements switch places
• C. A single element replaces another
• D. A decomposition reaction can occur

Answer: (B)

In a double replacement reaction, two compounds exchange their ions to form two new compounds. This is like two partners swapping partners—the positive ions from one compound pair with the negative ions from the other, and vice versa. An example is mixing sodium chloride and silver nitrate to get sodium nitrate and silver chloride: NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s). This shows how the ions switch partners to produce new substances, often with a precipitate forming.

The idea here is different from single replacement, where only one element switches places with another element in a compound, and from decomposition, where a single compound breaks down into simpler substances. The statement that two elements switch places captures the essence of two compounds exchanging parts to make new compounds.