Which of the following pairs will give displacement reactions?

Question

Which of the following pairs will give displacement reactions?

1. A. AgNO₃ solution and copper metal (Correct answer)
2. B. NaCl solution and copper metal
3. C. FeSO₄ solution and silver metal
4. D. MgCl₂ solution and aluminium metal

Correct Answer

Option A — AgNO₃ solution and copper metal

Detailed Solution & Explanation

The correct answer is AgNO₃ solution and copper metal.

Key Points

• A displacement reaction occurs when a more reactive metal displaces a less reactive metal from its salt solution.
• In silver nitrate (AgNO₃) solution with copper metal, copper is more reactive than silver, so copper displaces silver: Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag (the solution turns blue and silver deposits).
• The other pairs do not react: copper cannot displace sodium from NaCl (Na is far more reactive), silver cannot displace iron from FeSO₄ (Ag is less reactive than Fe), and aluminium is more reactive than magnesium, so it cannot displace Mg from MgCl₂.
• Hence the displacement reaction occurs with AgNO₃ and copper, option (A).

Additional Information

• Displacement follows the reactivity series: K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Ag > Au. A metal displaces any metal below it from solution.
• Copper sits above silver, so Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag proceeds, depositing silver and turning the solution blue.
• Metals below hydrogen — copper, silver, gold — cannot displace hydrogen from dilute acids, which is why copper does not react with dilute HCl.