Complete combustion of 750g of an organic compound provides 420g of...

$44gm$ ${CO}_{2}$ have $12gm$ carbon

So, $420gm{CO}_{2} ⇒ \dfrac{12}{44} \times 420$

$⇒ \dfrac{1260}{11}gm$ carbon

$⇒ 114 . 545$ gram carbon

So, $$ of carbon $= \dfrac{114 . 545}{750} \times 100$

$≃ 15 . 3$

$18gm{H}_{2}O ⇒ 2gm{H}_{2}$

$210gm ⇒ \dfrac{2}{18} \times 210$

$= 23 . 33gm{H}_{2}$

So, $$

$\approx 3$