The correct answer is B. Argon.
A monoatomic element is an element that exists as a single atom. Argon is a noble gas that is found in the Earth’s atmosphere. It is a colorless, odorless, and tasteless gas. Argon is used in many applications, including lighting, welding, and cryogenics.
Sulphur is a non-metal that is found in nature as a yellow solid. It is used in the production of sulfuric acid, which is a strong acid that is used in many industrial processes.
Hydrogen is a gas that is the lightest element in the universe. It is used in the production of ammonia, which is a fertilizer, and in the production of hydrogen fuel cells, which are used to power cars and other vehicles.
Oxygen is a gas that is essential for life. It is used in the process of respiration, which is how cells produce energy. Oxygen is also used in the production of steel and other metals.
In conclusion, the correct answer is B. Argon.