The correct answer is D. Sulphur.
Sulphur is a multi-atomic element because it exists as a molecule with eight atoms. The molecule is called sulphur octahydride, or $\ce{S8}$. It is a yellow, crystalline solid that is found in nature. Sulphur is used in a variety of products, including matches, gunpowder, and rubber.
Phosphorus is a non-metal that exists in three forms: white, red, and black. White phosphorus is the most common form and is highly flammable. It is used in matches, fireworks, and pesticides. Red phosphorus is less flammable than white phosphorus and is used in matches, explosives, and incendiary devices. Black phosphorus is the least reactive form and is used in lubricants, semiconductors, and batteries.
Chlorine is a greenish-yellow gas that is highly toxic. It is used in bleach, disinfectants, and insecticides. Argon is an inert gas that is used in light bulbs, welding, and cryogenics.
Therefore, the only multi-atomic element is sulphur.