Explanation

Reactivity with dilute HCl follows the standard reduction potentials: the more electropositive the metal, the more vigorous its reaction. Magnesium (E° ≈ −2.37 V) is the most reactive, followed by aluminium (E° ≈ −1.66 V), then zinc (E° ≈ −0.76 V), and iron (E° ≈ −0.44 V) is the least reactive of the four. The correct order is Mg > Al > Zn > Fe, so the answer is (A).