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Physics Guru is an online education and competitive examinations preparation portal founded by Manish Verma, an IIT Madras alumnus, providing learning resources for competitive examinations.

The emphasis is on conceptual understanding, analytical thinking and problem solving rather than simply memorising formulas and standard methods.

The objective is to help students understand what they are learning and develop the ability to solve problems they have not seen before.

Complete combustion of 750 g of an organic compound ....

Complete combustion of 750 g of an organic compound provides 420 g of $CO_2 $ and 210 g of $H_2 O $. The percentage composition of carbon and hydrogen in organic compound is 15.3 and _ _ _ _ respectively. (Round off to the nearest integer)

Solution

${n_{{H_2}O}} = \frac{{210}}{{18}} = \frac{{35}}{3}$

${n_H} = 2 \times {n_{{H_2}O}} = 2 \times \frac{{35}}{3} = \frac{{70}}{3}$

${m_H} = 1 \times \frac{{70}}{3}g$

% of H $ = \frac{{70 \times 100}}{{3 \times 750}} = 3.11\%  \approx 3\% $

Answer: 3