Complete combustion of 750 g of an organic compound provides 420 g of $$CO_2$$ and 210 g of $$H_2O$$. The percentage composition of carbon and hydrogen in organic compound is 15.3 and ________ respectively. (Round off to the Nearest Integer)

We are given that complete combustion of 750 g of an organic compound produces 420 g of $$CO_2$$ and 210 g of $$H_2O$$. We need to find the percentage of hydrogen in the compound.

First, let us find the mass of carbon. The molar mass of $$CO_2$$ is 44 g/mol, and each mole contains 12 g of carbon. So the mass of carbon in 420 g of $$CO_2$$ is $$\frac{12}{44} \times 420 = \frac{5040}{44} = 114.545$$ g.

The percentage of carbon is $$\frac{114.545}{750} \times 100 = 15.27\%$$, which rounds to approximately 15.3%, consistent with the given information.

Now, let us find the mass of hydrogen. The molar mass of $$H_2O$$ is 18 g/mol, and each mole contains 2 g of hydrogen. So the mass of hydrogen in 210 g of $$H_2O$$ is $$\frac{2}{18} \times 210 = \frac{420}{18} = 23.33$$ g.

The percentage of hydrogen is $$\frac{23.33}{750} \times 100 = 3.11\%$$.

Rounding off to the nearest integer, the percentage of hydrogen is $$\mathbf{3}$$.