How many of the following metals are extracted by self reduction process?
$P b, A u, M g, S n, F e, A l, A g, H g, N a, Z n, C u, C a$

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Solution

Self reduction or auto reduction process is reduction in presence of air without using external reducing agent.
Self reduction process is used in case of the sulfide ores of less electropositive metals like $H g, P b, C u$ . In this process the sulphide ores of these metals are heated in air to convert a part of it into oxides or sulphates which then reacts with the remaining sulphide ore to give metal and suphur dioxide.
Ex-
$2 H g S + 3 O_{2} \to 2 H g O + 2 S O_{2}$
$2 H g O + H g S \to 3 H g O + S O_{2}$

$P b S + 2 P b O \to 3 P b + S O_{2}$
$P b S + P b S O_{4} \to 2 P b + 2 S O_{2}$
$2 C u_{2} S + 3 O_{2} ⟶ 2 C u_{2} O + 2 S O_{2}$
$2 C u_{2} O + C u_{2} S ⟶ 6 C u + S O_{2}$

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