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JEE Advanced levelSingle correct optionDifficulty 3 of 3mt184

In a Parkes process, 2000 kg of molten lead contains 0.0300% silver by mass (600 g of Ag). Molten zinc (10.0 kg) is stirred in once and allowed to separate. At equilibrium the mass of Ag per kg in the zinc layer is 300 times that per kg in the lead layer. Treat the mass of lead as unchanged at 2000 kg. The mass of silver extracted into the zinc layer is

  1. A600 g
  2. B300 g
  3. C360 g
  4. D540 g

Answer: C

Let x g Ag go into zinc. Then x/10 = 300 x (600 - x)/2000, i.e. x = 1.5(600 - x) = 900 - 1.5x. So 2.5x = 900 and x = 360 g (60% of the silver). A single treatment does not remove it all, which is why zinc is added in portions.
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