Question

Which of the following reactions is an example of auto reduction?

• A.
• B.
• C.
• D.

Answer 1

The correct option is B

Option (a):

In auto-reduction, the reduction of less reactive metals like $Hg,Cu,Pb$ etc., take place by itself.

In this case Iron (II, III) oxide is reduced to Iron metal by carbon monoxide.

$F{e}_3+O_4+4CO\to 3Fe+4C{O}_2$

So, this is not an example of auto-reduction.

Option (b):

$C{u}_{2}o+C\to 2Cu+O$

In this case copper(I) oxide is reduced by carbon. So, this is not an example of auto-reduction.

Option (c):

$c{u}^{2+}\left(aq\right)+Fe\left(s\right)\to Fe\left(s\right)+Cu\left(s\right)+F{e}^{2+}\left(aq\right)$

In this case $C{u}^{2+}$ is reduced by iron metal. So, this is not an example of auto-reduction.

Option(d):

Metal is reduced by itself hence this process is known as auto reduction.

This reaction includes the reduction of copper(I) oxide by copper(I) sulphide.

$C{u}_{2}O+\frac{1}{2}C{u}_{2}S\to 3Cu+\frac{1}{2}S{O}_2$

In this process, copper is reduced by itself and the solidified copper is obtained.

So, the correct answer is option (D).