Question

A monatomic element:
A. nitrogen
B. hydrogen
C. radon
D. oxygen

Answer 1

Hint: The word monatomic is a combination of two words ‘mono’ and ‘atomic’ which means ‘single atom’. The term is usually used for gases, monatomic gas is a gas in which there is a single atom or atom is not bound to anyone.

Complete answer:
Let us discuss the options one by one:
A. Nitrogen: Molecular nitrogen (${\text{N}}_2$) is a chemical compound in which two nitrogen atoms are bound with a triple bond together. Nitrogen gas is a colourless, tasteless and inert gas at normal conditions. About 78% of Earth's atmosphere is nitrogen (${\text{N}}_2$).

B. Hydrogen: Hydrogen molecule is the simplest molecule having a covalent bond. It is formed by two hydrogen atoms, each having one electron. Two electrons are shared in the covalent bond. It is represented by ${\text{H}}_2$.

C. Radon: A chemical element with the symbol $\text{Rn}$ and atomic number 86. Radon is a radioactive and colourless noble gas. Radon’s most stable isotope is ${}^{222}\text{Rn}$. Radioactivity has been used to kill cancerous cells. Radon produced commercially is used in radiation therapy.

D. Oxygen: At standard temperature and pressure, two atoms of oxygen bound to form dioxygen have the formula ${\text{O}}_2$; which is a colourless and odourless diatomic gas. ${\text{O}}_2$ is paramagnetic. It produces a magnetic field due to the spin magnetic moment of the unpaired electrons in the molecule.
So, the correct answer is “Option C”.

Note:Every element is monatomic but here we are talking about the existence of that element in nature. Elements that form stable homonuclear diatomic molecules at standard conditions (STP) are hydrogen gas (${\text{H}}_2$), nitrogen gas (${\text{N}}_2$), oxygen gas (${\text{O}}_2$) and chlorine gas ($\text{C}{\text{l}}_2$). The noble gases (like krypton, xenon, radon and other) are gases also stable at STP, but they exist as monatomic elements in nature.