0.2 g of an organic compound on complete combustion produces 0.18 g of water, then the percentage of hydrogen in it is:

We know, in 1mol i.e. 18g of ${\mathrm{H}}_2\mathrm{O}$, hydrogen content is = 2 g
Therefore, in 1 g ${\mathrm{H}}_2\mathrm{O}$, hydrogen content will be = $\frac{2}{18}$g
Thus, in 0.18 g $H_{2}O$, hydrogen content will be = $\frac{2}{18} X 0.18$ g = 0.02 g

From this, we can assume that;
0.2 g of organic compound gives = 0.02 g hydrogen
1 g of organic compound gives = $\frac{0.02}{0.2}$g hydrogen
Therefore, 100g of organic compound gives = $\frac{0.02}{0.2} X 100 = 10 \%$ hydrogen.

Thus, the correct answer is option (B) 10.