Which of the following is not prepared by Kolbe's electrolytic process?
Correct option is A. $$C_{3}H_{8}$$
Hydrocarbons prepared by Kolbe's Electrolysis contains even number of carbons.
Of the above given compounds, only $$\mathrm{C_3H_8}$$ has odd number of carbons in it. So, it can't be prepared by Kolbe's electrolysis process.
Hence, Option "A" is the correct answer.