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Q98 (CDS-I/2024) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Basic chemical principles Answer Verified

Which one of the following is the correct order of reactivity of Mg, Al, Zn and Fe with HCl? (a) Mg > Al > Zn > Fe (b) Mg > Al > Fe > Zn (c) Zn > Fe > Mg > Al (d) Fe > Al > Zn > Mg

Result
Your answer: —  Â·  Correct: A
Explanation

The reactivity of metals with dilute hydrochloric acid (HCl) is determined by their position in the activity series and their ability to displace hydrogen ions. According to experimental observations, magnesium (Mg) reacts most vigorously, showing the fastest rate of bubble formation and the most exothermic reaction [1]. Aluminium (Al) follows magnesium in reactivity; although it forms a protective oxide layer, it reacts more readily than zinc once the layer is breached. Zinc (Zn) reacts steadily with HCl to produce zinc chloride and hydrogen gas [1]. Iron (Fe) reacts more slowly than zinc, forming iron(II) chloride [1]. Therefore, the correct decreasing order of reactivity is Mg > Al > Zn > Fe [2]. This sequence aligns with the standard activity series where magnesium is the most electropositive among these four, and iron is the least [2].

Sources

  1. [1] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > Activity 3.11 > p. 44
  2. [2] Science , class X (NCERT 2025 ed.) > Chapter 3: Metals and Non-metals > 3.2.5 The Reactivity Series > p. 45
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