If metal A displaces metal B from an aqueous solution of its salt, which conclusion is correct?

Correct answer: Metal A is more reactive than metal B

A displacement reaction occurs when a more reactive metal removes a less reactive metal from its salt solution. If A displaces B from an aqueous solution of a B salt, A must be above B in the reactivity series and therefore is more reactive. Hence option D is correct. If B were more reactive, it would remain in solution while A could not displace it; equal reactivity would not produce this displacement.