Which one of the following is the correct reactivity order of metals reacting with dilute HCl?
- A.Mg > Al > Zn > Fe
- B.Mg < Al < Zn < Fe
- C.Mg > Zn > Fe > Al
- D.Fe > Mg > Al > Zn
Correct answer
Explanation
The correct answer is A, Mg > Al > Zn > Fe. This is the order in which these metals stand in the reactivity series, and it matches how vigorously they release hydrogen from dilute hydrochloric acid.
The reactivity series runs K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au. With dilute HCl, magnesium reacts most vigorously and gives a fast stream of hydrogen bubbles; aluminium reacts strongly once its thin protective oxide layer is removed; zinc reacts steadily, which is why it is used to prepare hydrogen in the laboratory; and iron reacts slowly. In each case the metal forms its chloride and hydrogen gas, for example Mg + 2HCl → MgCl₂ + H₂. Copper, which lies below hydrogen, does not react at all.
Option B is wrong because it reverses the correct order. Option C is wrong because aluminium is more reactive than zinc and iron. Option D is wrong because iron is the least reactive of the four, not the most.
Exam tip: remember the series as Mg > Al > Zn > Fe > Pb > H > Cu; metals below hydrogen do not give H₂ with dilute acids.
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