0.25 g of an organic compound "A" containing carbon, hydrogen and oxygen was analysed using the combustion method. There was an increase in mass of $$CaCl_{2}$$ tube and potash tube at the end of the experiment. The amount was found to be 0.15 g and 0.1837 g, respectively. The percentage of oxygen in compound A is __ %. (Nearest integer)
(Given: molar massing $$mol^{-1}$$ H : 1, C : 12, O : 16)

Mass of compound = 0.25 g, increase in CaCl$$_2$$ tube (water) = 0.15 g, increase in potash tube (CO$$_2$$) = 0.1837 g.

Mass of carbon.

$$\text{Mass of C} = \frac{12}{44} \times 0.1837 = 0.05010$$ g

Mass of hydrogen.

$$\text{Mass of H} = \frac{2}{18} \times 0.15 = 0.01667$$ g

Mass and percentage of oxygen.

Mass of O = $$0.25 - 0.05010 - 0.01667 = 0.18323$$ g

Percentage of oxygen = $$\frac{0.18323}{0.25} \times 100 = 73.3\% \approx 73\%$$

The answer is 73.