Question

Which substance, when dissolved in water, forms a solution that conducts an electric current?

Answer 1

Missing question: 
(1) C2H5OH (3) C12H22O11
(2) C6H12O6 (4) CH3COOH.

Answer is: 4) CH₃COOH, acetic acid.
In water, acetic acid dissociates on ions, so it can conduct electricity:
CH₃COOH(aq) ⇄ CH₃COO⁻(aq) + H⁺(aq).
When we put electrodes (cathode and anode) in acetic acid solution, positive and negative ions migrate to electrodes.
Negative acetate ions go to positive electrode and gives electrons to electrode.
Positive hydrogen ions go to negative electrode and gain electrons.