10 " mL of " a gaseous hydrocarbon is exploded with 100 " mL of " oxygen. The residual gas on cooling is found to measure 95 mL, of which 20 mL is absorbed by caustic soda and the remaining by alkaline pyrogallol. The formula of the hydrocarbon is
(a). `CH_4`.
(b). `C_2H_6`
(c). `C_2H_4`
(d). `C_2H_2`

Options

A. `C_2H_6`
B. `C_2H_4`
C. `C_3H_8`
D. `C_3H_6`

Answer

B

Explanation

`C_xH_y+(x+(y)/(4))O_2rarrxCO_2+(y)/(2)H_2O`
`7.5ml 7.5(x+(y)/(4))ml 7.5x ml _`
Volume of `CO_2=15ml`
`7.5x=15,x=2`
Volume of `O_2` (absorbed in pyrogallol) `=28.5-15`
`=13.5ml`
Volume of `O_2` (used) `=36-13.5=22.5ml`
`7.5(x+(y)/(4))=12.5`
Solving for `y`, putting `x=2,y=4`
Hence the formula `=C_2H_4`