General Principles and Processes of Isolation of Elements
The auto-reduction process is not used in the metallurgy of:
Correct Answer: Option(d)
Solution: Auto-reduction or air reduction is very popular reaction in metallurgy.
It is a process in which sulphide ores of less electropositive metals like Hg, Pb, Cu etc., are heated in air so as to convert part of the ore into oxide or sulphate which then reacts with the remaining of sulphide ore in absence of air to give the metal and sulphur dioxide.
Hence, option D is correct.