Which one of the following is not a monatomic element ?

Which one of the following is not a monatomic element ?

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Copper

Helium

Iodine

Barium

Answer is Right!

Answer is Wrong!

This question was previously asked in

UPSC NDA-2 – 2019

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The correct answer is C) Iodine.

A monatomic element is an element that exists stably as individual atoms rather than in molecules composed of two or more atoms. Helium (He) is a noble gas and exists as single atoms, making it monatomic. Copper (Cu) and Barium (Ba) are metals that exist as lattices of individual atoms in their solid state. Iodine (I) is a halogen that exists as a diatomic molecule ($I_2$) in its standard solid state and gaseous state (when it sublimes). Thus, Iodine is not a monatomic element; it is diatomic.

Noble gases (He, Ne, Ar, Kr, Xe, Rn) are the most common examples of naturally occurring monatomic elements. While metals exist as individual atoms in their solid structure, the term “monatomic” is most frequently used to contrast with diatomic or polyatomic molecular elements like $O_2$, $N_2$, $S_8$, $P_4$, and halogens ($F_2$, $Cl_2$, $Br_2$, $I_2$). Among the given options, Iodine is the only one that exists as a diatomic molecule in its elemental form.

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