Which represents a double replacement reaction and would occur?

In a double replacement reaction, the positive ions exchange partners. In choice A, Na⁺ and Ca²⁺ switch partners, forming NaCl and CaCO₃. Calcium carbonate is an insoluble solid, so it precipitates from the solution and makes the reaction occur. The other proposed exchanges do not form a precipitate, gas, or weak electrolyte to drive a reaction.

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