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The auto-reduction process is not used in the metallurgy of;
(A) \[Hg\]
(B) $Cu$
(C) $Pb$
(D) $Fe$

Last updated date: 14th Jun 2024
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Hint- Auto-reduction process is a reaction used in the metallurgy of some metals. It is a quite famous reaction which is applicable to the sulphide ores of the less electropositive metals like \[Hg,Pb,Cu\] etc.

Complete step by step solution:
Hence in the above options given we see that \[Hg,Cu,Pb\] are less electropositive and can be obtained by auto-reduction of their ores.
Only $Fe$ does not fall in this category, that means $Fe$ can’t be obtained from its ore by an auto-reduction process.
So, the auto reduction process is not used in the metallurgy of the iron, $Fe$.

Hence option (D) is the correct answer.
> It is a process in which sulphide ore of some less electropositive metals are heated in the presence of air. This is done to convert some part of the ore into the oxide or sulphate. Then this converted part that is oxide or sulphate will react with the remaining part of the sulphide ore in the absence of air to give metal and sulphur dioxide.
For example-
For copper (Cu) ore
> For the extraction of the copper from its sulphide ore, the ore is subjected to the partial roasting in the presence of air to get its oxide:
$2C{u_2}S + 3{O_2} \to 2CuO + 2S{O_2}$
Now the supply of the air is cut off and the temperature is raised, then the rest of the sulphide ore will react with the oxide and form the metal $Cu$.
$C{u_2}S + 2CuO \to 6Cu + S{O_2}$

Note-Here in this process of metallurgy to extract metals from its ore, there is no any external reducing agent used for the reduction, this is the reason we call it an auto-reduction process. This process is also called an air reduction process, because in this process there are two steps, one is with air and the second step is in absence of air, so in this way the air is getting reduced in the second step.