Which of the following substances decomposes when an electric current is passed through it?

Out of the given options, tetrachloromethane is the substance that decomposes when an electric current is passed through it. Tetrachloromethane, also known as carbon tetrachloride, is a covalent compound with the chemical formula CCl₄. It is a non-conductor of electricity in its pure form, but when it is mixed with small amounts of impurities, it becomes a conductor of electricity. When an electric current is passed through it, tetrachloromethane undergoes electrolysis, which breaks down the C-Cl bonds and forms various products, including chlorine gas and phosgene gas. On the other hand, glucose solution, zinc rod, and hydrochloric acid do not decompose when an electric current is passed through them. Glucose is a covalent compound that does not dissociate into ions in solution, so it cannot undergo electrolysis. Zinc is a metal and a good conductor of electricity, but it does not undergo any significant chemical reaction when an electric current is passed through it. Hydrochloric acid is an aqueous solution of hydrogen chloride, which dissociates into H⁺ and Cl^- ions in solution. However, it is not a good conductor of electricity because the concentration of ions is relatively low.