5 " mL of " a gas A containing only C and H was mixed with an excess of `O_2` (30 mL) and the mixture was exploded by means of electric sperk. After explosion, the remaining volume of the mixed gases was 25 mL. On adding a concentrated solution of KOH, the volume further diminished to 15 mL. The residual gas was pure oxygen, The molecular formula of the gas A is.

Options

A. `C_(2)H_(6)`
B. `C_(3)H_(6)`
C. `C_(2)H_(4)`
D. None of these

Answer

C

Explanation

`{:(C_(x) H_(y) (g) ,+, (x +(y)/(4)) O_(2) (g) ,rArr,xCO_(2) (g) + (y)/(2) H_(2)O(1)),(1ml,,(x + (y)/(4)) ml,,x ml):}`
Contraction in volume due to combustion `=5 (1 + x + (y)/(4) -x) = 5 + 30 -25 = 10 rArr y = 4`
Contraction due to `KOH = 25 -15 = 10 = 5x rArr x = 2 rArr` Molecular formula `=C_(2)H_(4)`