Which of the following statements about displacement reaction is correct?

Step 1: Analyze the question The question asks which statement about a displacement reaction is correct. It is a concept question about the reactivity (electrochemical) series.

Step 2: The concept In a displacement reaction, a more reactive element takes the place of a less reactive element in a compound. For metals, reactivity means how readily the metal loses electrons to form positive ions, which is the same as being more electropositive.

Reactivity series (highest to lowest): K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au

Step 3: Example Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

• Zinc is more electropositive than copper.
• Zinc loses electrons (it is oxidised): Zn → Zn²⁺ + 2e⁻
• Cu²⁺ gains electrons (it is reduced): Cu²⁺ + 2e⁻ → Cu
• The blue colour of the solution fades and reddish-brown copper is deposited.

The reverse (Cu added to ZnSO₄ solution) gives no reaction, because copper is less electropositive and cannot displace zinc.

Step 4: Check each option

• A. A more electropositive element displaces a less electropositive one. ✔ Correct.
• B. Wrong. This is the reverse of what happens.
• C. Wrong. The position in the reactivity series determines whether the reaction occurs.
• D. Wrong. Displacement reactions go to completion when feasible. They are not restricted to equilibrium.

Answer: A

Exam tip: Remember "the stronger pushes out the weaker." A metal higher in the reactivity series displaces the ones below it from their salt solutions. The same idea applies to halogens: Cl₂ displaces Br⁻ and I⁻ from solutions of their salts, because chlorine is more reactive than bromine or iodine.