A mixture of CaCO and MgCO loses on strong heating (both decompose completely to the oxide and CO). The mass of CaCO in the mixture is (Ca , Mg , C , O )

Answer and explanation

Correct answer: B.

  1. Step 1: Determine the moles of liberated during thermal decomposition. The mass loss is entirely due to expelled gaseous : .
  2. Step 2: Thermal decomposition yields one mole of per mole of carbonate: and . Thus .
  3. Step 3: Let be the mass of in grams, so the mass of is . Express the total moles using molar masses (, ): . Clearing denominators by multiplying by gives .
Answer
.
Why not the others: assumes an equimolar ratio based on average molar mass rather than solving the stoichiometric decomposition.

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