Final answer:
CH4 (methane) is the substance that is NOT an electrolyte; it is a non-polar compound that does not ionize in water, thus does not conduct electricity when dissolved.
Step-by-step explanation:
Identification of Non-electrolyte Substance
The substance that is NOT an electrolyte among the listed options is (c) CH4 (methane). An electrolyte is a substance that dissolves in water to give a solution that conducts an electric current. For a substance to act as an electrolyte, it must be either ionic, like salts, or a polar compound that ionizes in aqueous solution. Methane, CH4, is a non-polar compound and does not ionize in water, therefore it does not conduct electricity when dissolved and is considered a nonelectrolyte.
Other listed substances, (a) HCl (hydrochloric acid), (b) NH4NO3 (ammonium nitrate), and (d) K2SO4 (potassium sulfate), are all electrolytes as they dissolve in water to form ions which can conduct electricity.