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Auto-reduction process is :
(1) A    (2) B    (3) both    (4) none

Answer: (2)
Explanation:
Although Pb can be extracted either by using A or B. In A, the 2nd step is called as carbon reduction and in B, the 2nd step is called as “Self-Reduction” or “Auto-reduction” Self-reduction is a type of reduction reaction in which a substance is reduced by its own product(s) without the addition of an external reducing agent. In other words, the substance being reduced acts as its own reducing agent. Hence in B when PbO was roasted, PbO was formed and which in turn react again with PbS to form Pb and So2 gas.

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