Question

Which of the following pairs will give displacement reactions?
A.$\text{NaCl}$ solution and copper metal
B.$\text{MgC}{{\text{l}}_{\text{2}}}$ solution and aluminium metal
C.$\text{FeS}{{\text{O}}_{4}}$ solution and silver metal
D.$\text{AgN}{{\text{O}}_{3}}$ solution and copper metal

Answer 1

Hint:The displacement of one metal by the other in a reaction is dependent on the position of the metals in the electrochemical series of metals. Those above in the series can get reduced to replace the metal is the salt.

Complete step by step answer:
$\text{NaCl}$ Solution and copper metal- sodium is placed much higher than copper in the electrochemical series so copper cannot replace sodium by getting oxidised itself. Hence this reaction is not possible.
$\text{MgC}{{\text{l}}_{\text{2}}}$ Solution and aluminium metal-as aluminium is lower in the electrochemical series than magnesium, so it cannot reduce magnesium chloride and hence this reaction is also not feasible.
$\text{FeS}{{\text{O}}_{4}}$ Solution and silver metal- as iron is above silver in the electrochemical series, so silver cannot displace iron from its salt and get oxidized itself.
$\text{AgN}{{\text{O}}_{3}}$ Solution and copper metal- as copper is placed above silver in the electrochemical series, so it will displace silver from the silver nitrate, $\text{AgN}{{\text{O}}_{3}}$ and get oxidized as cuprous ions. Hence this reaction is feasible.

So, the correct answer is option D.

Note:
The electrochemical series is built up by arranging various redox equilibriums in order of their standard electrode potentials. The elements with most negative electrode potential values, having the least tendency to get reduced are placed on the top while those with positive values are placed at the bottom having the highest tendency to get reduced.