20.0 g of magnesium carbonate sample decomposes on heating to give carbon dioxide and 8.0 g of magnesium oxide. What will be the percentage purity of magnesium carbonate in the sample?

Options

A. 75
B. 96
C. 60
D. 84

Answer

D

Explanation

`underset(84 mu)underset((24+12+48)mu)(MgCO_(3)) to underset( 40 mu) underset((24+16) mu)(MgO + CO_(2))`
40 g of magnesium oxide produced by = 84g of pure sample
8 g of magnesium oxide produced ` = (84)/(40) xx 8`
= 16.8g of pure sample
% purity of sample ` = (16.8)/(20)xx 100`
= 84.0