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_(4)`
B. `C_(2)H_(6)`
C. `C_(3)H_(6)`
D. `C_(3)H_(8)`

Answer

A

Explanation

`{:(C_(x)H_(y)(g),+(x+(y)/(4))O_(2)(g),rarrx CO_(2),(g)+(y)/(2)H_(2)O(1)),(1ml,(x+(y)/(4))ml,xml,-),(5ml,5(x+(y)/(4))ml,5x ml,-):}`
Volume of gases remaining (i.e., volume of `CO_(2)` + volume of `O_(2)` unreacted = 25 ml
Volume remaining after absorbing KOH = 15 ml
Volume absorbed by KOH = volume of `CO_(2) = 25 - 15 = 10 ml`.
Volume of `CO_(2) implies 5x = 10 ml`, x = 2
Volume of `O_(2)` taken = 30 ml
Volume of `O_(2)` reached `= 30 - 15 = 15 ml`
`:. 5(x + (y)/(4)) = 15`
`5(2 + (y)/(4)) = 15`
y = 4
Formula of gas (A) `= C_(2)H_(4)` (Ethene).