Which of the following statement(s) is (are) true?

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In the porocess of precipitation of silver from sodium dicyanidoargentate (I), the zinc acts as reducing agent as well as complexing agent.

In process of the roasting, the copper pyrite is converted into a mixture of ${Cu}_{2} S$ and FeS which, in turn, are partially oxidised.

Limonite, haematite and magnesite are ores of iron

Tin and lead both are extracted from their ores by self-reduction.

answer is A.

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Detailed Solution

The zinc serves as a complexing and reducing agent during the precipitation of silver from sodium dicyanido argentate (I), and during roasting, copper pyrite is changed into a combination of ${Cu}_{2} S$ and FeS, which are then partly oxidised.

Zinc serves as a complexing and reducing agent during the precipitation of silver sodium dicyano argentate (l). Silver's oxidation state shifts from +1 to 0. The reaction is having follows,

$2 NaAg (CN)_{2} + Zn \to 2 Ag + {Na}_{2} Zn (CN)_{4}$

The copper pyrites are changed during the roasting process into a combination of ${Cu}_{2} S$ and FeS, which are then partly oxidized. The following reaction will obtain,

$\begin{array}{l} 2 {CuFeS}_{2} + O_{2} \to {Cu}_{2} S + 2 FeS + {SO}_{2} \\ 2 {Cu}_{2} S + 3 O_{2} \to 2 {Cu}_{2} O + 2 {SO}_{2} \\ 2 FeS + 3 O_{2} \to 2 FeO + 2 {SO}_{2} \end{array}$