0. 765g of an acid gives 0. 535g of CO _ 2 and 0. 138g of H _ 2 O ....

$$ for ${CO}_{2}$

$∵ 0. 765g$ of acid gives ${CO}_{2} = 0. 535g$

$∴ 100g$ of acid gives ${CO}_{2} = \dfrac{0. 535 \times 100}{0. 765}$

$$ of ${CO}_{2} = 70. 00$

$$ for carbon

$∵ 44g$ of ${CO}_{2}$ gives, $C = 12g$

$∴ 70g$ of ${CO}_{2}$ gives, $C = \dfrac{12 \times 70}{44}$

$= 19. 09g$

$∴$ of carbon $= 19. 00$

Similarly,

(i) for hydrogen&

$$ of ${H}_{2}O$

$⇒ \dfrac{0. 138 \times 100}{0. 765}$

$= 18. 03 = 18. 00$

$$ of Hydrogen

$⇒ \dfrac{2 \times 18}{18} = 2. 00$

Hence ratio of carbon and hydrogen is $19: 2$