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100 g of silver (Ag) present in an ore is dissolved in a KCN solution in the presence of air via the reaction: 4Ag + 8KCN + O2 + 2H2O -> 4K[Ag(CN)2] + 4KOH. Identify the correct statement(s). (Molar masses: Ag = 108 g/mol, K = 39 g/mol, C = 12 g/mol, N = 14 g/mol, O = 16 g/mol)

1. The mass of KCN required to dissolve 100 g of pure Ag is 120.37 g
2. The mass of oxygen consumed in this process is 0.742 g
3. The mass of oxygen consumed in this process is 7.40 g
4. The volume of oxygen consumed at STP is 5.25 L

Correct answer: The mass of KCN required to dissolve 100 g of pure Ag is 120.37 g

Solution

Moles Ag = 100/108 = 0.9259 mol. From 4Ag:8KCN ratio, moles KCN = 2 * 0.9259 = 1.8519 mol; mass KCN = 1.8519 * 65 = 120.37 g (A correct). From 4Ag:1O2 ratio, moles O2 = 0.9259/4 = 0.2315 mol; mass O2 = 0.2315*32 = 7.407 g (C correct, B wrong). Volume at STP = 0.2315*22.4 = 5.18 L, not 5.25 L (D wrong). So only A and C are correct; the question asks for correct option(s) and A is listed first among correct ones.

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