Which of the following pairs will give displacement reactions?

(a) NaCl solution and copper metal

(b) MgCl ₂ solution and aluminium metal

(c) FeSO ₄ solution and silver metal.

(d) AgNO ₃ solution and copper metal.

Answer

We know that, 

• More reactive metals displace less reactive metals from their salts. 
• When a less reactive metal is added to the solution of a more reactive metal , no reaction takes place ,

Let's consider all options

1. (a) NaCl solution and copper metal
   Cu is less reactive than Na , therefore it cannot displace Na.
   
   
2. (b) MgCl2 solution and aluminium metal
   Al is less reactive than Mg , therefore it cannot displace Mg.
   
   
3. (c) FeSO4 solution and silver metal
   Ag is less reactive than Fe , therefore it cannot displace Fe..
   
   
4. (d) AgNO3 solution and copper metal.
   Cu is more reactive than Ag , therefore displacement takes place .
   The reaction can be given as :

Cu + 2AgNO ₃ = Cu(NO ₃ ) ₂ + 2Ag .

So, the correct answer is (d)