Identify less reactive element from the following:

Hint: Many atoms in molecules are more stable while the valence shell comprises essentially eight electrons, which is referred to as a "stable octet." Non-bonding electrons and electrons in chemical bonds between atoms are both counted.

Complete answer:
The octet rule is a chemical rule of thumb that illustrates the idea that main-group elements appear to bind in such a way that each atom has eight electrons in its valence shell, resulting in an electronic structure similar to that of a noble gas.
\[_8{Y^{16}}\] Refers Oxygen.
Electronic Configuration = 2, 6
Absence of octet configuration. Hence it is not stable, more reactive
Oxygen is a chemical element with the atomic number 8 and the letter O. It is a highly reactive nonmetal and an oxidising agent that readily forms oxides with certain elements and other compounds. It belongs to the chalcogen group of the periodic table.
\[_{10}{Y^{20}}\] refers Neon
Electronic Configuration = 2, 8
Presence of octet configuration. Hence it is most stable, least reactive
Neon is a chemical element with the atomic number 10 and the symbol Ne. It's classified as a noble gas. Under normal conditions, neon is a colourless, odourless, inert monatomic gas with a density of around two-thirds that of air.
\[_{11}{Y^{23}}\] refers Sodium
Electronic Configuration = 2, 8, 1
Absence of octet configuration. Hence it is not stable, more reactive
The chemical element sodium has the symbol Na and the atomic number 11. It's a soft, silvery-white metal with a high reactivity. Sodium belongs to the periodic table's group 1 as an alkali metal. It has only one stable isotope, $^{23}Na$. The free metal isn't found in nature, so it has to be made from additives.
\[_9{Y^{19}}\] refers Fluorine
Electronic Configuration = 2, 7
Absence of octet configuration. Hence it is not stable, more reactive
Fluorine is a chemical element with the atomic number 9 and the symbol F. It is the lightest halogen that appears as an extremely radioactive, pale yellow diatomic gas in normal conditions. It is highly reactive as the most electronegative element, reacting with all other elements except argon, neon, and helium.
Hence, option B is correct.

Note:
Neon is a chemical element with the atomic number 10 and the symbol Ne. It's classified as a noble gas. Under normal conditions, neon is a colourless, odourless, inert monatomic gas with a density of around two-thirds that of air.