UPSC CDS 2 2019 GK Paper

Concept:Monatomic elements exist as single atoms in their standard state due to a stable electron configuration.Explanation:Helium ($\mathrm{He}$) is a noble gas with a full outer shell of $2$ electrons.It does not need to bond with other atoms to become stable.Thus, it is naturally monatomic.Hydrogen ($\mathrm{H}_2$) exists as diatomic molecules in its elemental form.Sulphur typically forms $\mathrm{S}_8$ rings (octatomic).Phosphorus exists as $\mathrm{P}_4$ molecules (tetratomic).Only helium among the given options is monatomic.Answer:D. Helium