The fact that when in solution C₂H₅OH conducts electricity means that it is an electrolyte so you can automatically cross out A and C (the definition of an electrolyte is a substance that will conduct electricity when in a solution). I think the correct answer is B due to the -OH group (the - indicates a covalent bond) which allows the molecule to give up a proton (H⁺).
I hope this helps. Let me know if anything is unclear.
