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A 4.0 molar aqueous solution of NaCl is prepared, and 500 mL of this solution is electrolysed completely. Chlorine gas is evolved at one electrode. Assuming all the chloride ions are discharged, the total number of moles of Cl2 gas liberated is: (1 Faraday = 96500 C)

1. (A) 0.5
2. (B) 1.0
3. (C) 2.0
4. (D) 3.0

Correct answer: (B) 1.0

Solution

Moles of NaCl = molarity * volume(L) = 4.0 * 0.500 = 2.0 mol, giving 2.0 mol of Cl⁻ ions. At the anode the oxidation is 2 Cl⁻ -> Cl2 + 2 e⁻, so 2 moles of chloride produce 1 mole of chlorine gas. Hence 2.0 mol Cl⁻ yields 1.0 mol Cl2.

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