Silver metal in ore is dissolved by potassium cyanide solution in the presence of air by the reaction
$4 A g + 8 K C N + O_{2} + 2 H_{2} O \to 4 K A g {(C N)}_{2} + 4 K O H$

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The amount of KCN required to dissolve 100g of pure Ag is 120g.

The amount of oxygen used in this process is 0.742g

The amount of oxygen used in this process is 7.40g

The volume of oxygen used at STP(1 atm , 273 K) is 5.20 lit.

answer is A, C, D.

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Detailed Solution

$4 A g + 8 K C N + O_{2} + 2 H_{2} O \to 4 k [A g {(C N)}_{2}] + 4 K O H$
$\Rightarrow 4 \times 108 g o f A g r e a c t s w i t h 8 \times 65 g o f K C N$
$100 g o f A g r e a c t s w i t h \frac{8 \times 65}{4 \times 108} \times 100 = 120$
Hence to dissolve 100g of Ag, the amount of KCN required = 120 g
Hence, statement (A) is correct
$\Rightarrow 4 \times 108 g o f A g r e q u i r e 32 g o f O_{2}$
$\Rightarrow 100 g o f A g r e q u i r e = \frac{32 \times 100}{4 \times 108} = 7.14 g$
$H e n c e, c h o i c e (C) i s c o r r e c t$
$H e n c e, v o l u m e o f O_{2} r e q u i r e d$
$= \frac{7.4}{32} \times 22.4 = 5.20 = l i t r e$
$H e n c e (A), (C), (D) a r e c o r r e c t w h i l e (B) i s i n c o r r e c t$