Which of the following reaction is an example of autoreduction ?

Options

A. `Fe_(2)O_(4) + 4CO to 3Fe + 4CO_(2)`
B. `Cu_(2)O + C to 2Cu + CO`
C. `Cu_((aq))^(2+) + Fe_((s)) to Cu_((s)) + Fe_((aq))^(2+)`
D. `Cu_(2)O + (1)/(2)Cu_(2)S to 3Cu + 1/2 SO_(2)`

Answer

D

Explanation

The sulphide ores of certain less electropositive metals like those of Hg, Pb, Cu, etc. When heated in air bring about the conversion of a part of the sulphid ore to oxide or sulphide which then reacts with the remaining sulphide to give the metal and `SO_(2)` . No external reducing agent is used in this process.
`2Cu_(s)S +3O_(2) to 2Cu_(2)O + 2SO_(2)`
`2Cu_(2)O + Cu_(s)S to 6Cu + SO_(2)`