Question

Addition of ${ SnCl }_{ 2 }$ to ${ HgCl }_{ 2 }$ gives ppt:
A. White turning to grey
B. Black turning to white
C. White turning to red
D. None of these

Answer 1

Redox reactions are those reactions in which oxidation and reduction occur simultaneously. The reaction of ${ SnCl }_{ 2 }$ with ${ HgCl }_{ 2 }$ is an oxidation-reduction reaction.

Complete answer:
When ${ SnCl }_{ 2 }$ reacts with ${ HgCl }_{ 2 }$, the following reaction will take place:
${ 2HgCl }_{ 2 }{ +SnCl }_{ 2 }{ \rightarrow 2HgCl+SnCl }_{ 4 }$
This addition of ${ SnCl }_{ 2 }$ to ${ HgCl }_{ 2 }$ gives white turning to a grey ppt. ${ HgCl }_{ 2 }$ formed is white.
On further reaction, HgCl is converted to Hg which is grey due to further reduction.
In this reaction, ${ SnCl }_{ 2 }$ acts as an oxidizing agent while ${ HgCl }_{ 2 }$ acts as a reducing agent.
Hence, the correct option is A.

Additional Information:
The substances that are reduced (provide oxygen or remove hydrogen) in course of the reaction are called oxidizing agents. These substances oxidize different chemicals in the reaction and are reduced simultaneously.
On the other hand, the substances that are oxidized (remove oxygen or provide hydrogen) are called reducing agents.
Oxidation is defined as a procedure that involves the addition of oxygen or a lost hydrogen.
The reduction is defined as a procedure that involves the addition of hydrogen or a lost oxygen.

Uses of redox reactions:
Combustion of coal to generate electricity.
Rusting of iron objects, in presence of atmospheric oxygen and water.

Note: The possibility to make a mistake is that here ${ SnCl }_{ 2 }$ is getting oxidized, not reduced and ${ HgCl }_{ 2 }$ is getting reduced, not oxidized.