Correct Option: D  [ Argon ]
Remark:
Argon (Ar) is an inert gas, also known as a noble gas. It belongs to Group 18 of the periodic table, whose elements are characterized by complete outer electron shells, making them chemically unreactive. Argon constitutes about 0.93% of the Earth's atmosphere and is widely used in electric bulbs, welding, and in creating inert environments for chemical reactions.
Other options (for context)
- Hydrogen: Highly reactive and combustible gas.
- Nitrogen: Relatively less reactive but not inert; forms compounds like ammonia.
- Oxygen: Highly reactive gas essential for combustion and respiration.