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            2.9 g

Explanation:

The balanced chemical equation is

CaCO3  > CaO + CO2

The amount of CaCO3 is,

32.4 g - 27.3 g = 5.1 g

Change grams to moles,

Mole = 5.1 g / 100.09 g/mol

Moles = 0.0509

The mole ratio of CaCO3 and CaO is 1:1. Hence, 0.0509 mole of CaO will produce.

Now, convert 0.0509 mole to grams as,

Mass = Moles x M.Mass

Mass = 0.0509 mole x 56.08 g/mol

Mass = 2.8575 g or 2.9 g

pure substance: iron,copper

impure substance: water,charcoal

a is the correct answer