The correct choice is petrolatum because it is a hydrocarbon, specifically a semi-solid mixture of hydrocarbons derived from petroleum. Hydrocarbons are organic compounds consisting exclusively of carbon (C) and hydrogen (H) atoms. Petrolatum contains long chains of carbon and hydrogen, making it a classic example of a hydrocarbon.
Potassium chloride is an ionic compound composed of potassium and chlorine, with no carbon or hydrogen content. Sodium hydroxide is a strong base made of sodium, oxygen, and hydrogen, but it does not have the carbon characteristic of hydrocarbons. Stearic acid is a saturated fatty acid that contains carbon, hydrogen, and oxygen; although it has a hydrocarbon structure, it is not classified purely as a hydrocarbon due to the presence of oxygen in its carboxylic acid functional group. Thus, among the options provided, petrolatum stands out as the only genuine hydrocarbon.