Question

Which Elements are non reactive?

• A. Oxygen
• B. Hydrogen
• C. Helium
• D. Carbon

Answer 1

The correct option is C

Helium

The explanation for the correct answer

(C) Helium

1. Helium $\left(\mathrm{He}\right)$ is the element of group 8 and period 1 having the Atomic number 2.
2. The electronic configuration of Helium $\left(\mathrm{He}\right)$ is $1{\mathrm{s}}^2$.
3. As the valence shell of Helium $\left(\mathrm{He}\right)$ is fully filled therefore it is unreactive.
4. Helium $\left(\mathrm{He}\right)$ is an inert gas and inert gases are generally unreactive.

The explanation for the incorrect answer

(A) Oxygen

1. Oxygen $\left(\mathrm{O}\right)$ is the element of group 16 and period 2 having the atomic number of 16.
2. The electronic configuration of Oxygen $\left(\mathrm{O}\right)$ is $\left[\mathrm{He}\right]2s^{2}2p^4$.
3. As the valence shell of Oxygen $\left(\mathrm{O}\right)$ is not completely filled, it needs two more electrons to achieve noble gas configuration and Thus Oxygen $\left(\mathrm{O}\right)$ is very reactive.
4. Oxygen $\left(\mathrm{O}\right)$ being electronegative it is highly reactive.

(B)Hydrogen

1. Hydrogen$\left(\mathrm{H}\right)$ is the first element of periodic table having the atomic number of 1.
2. The electronic configuration of Hydrogen$\left(\mathrm{H}\right)$ is $1{\mathrm{s}}^1$.
3. As the valence shell oh Hydrogen$\left(\mathrm{H}\right)$ has only one electron and thus hydrogen can lose this electron easily and becomes ${\mathrm{H}}^{+}$.
4. Thus Hydrogen$\left(\mathrm{H}\right)$ being electropositive is highly reactive.

(D) Carbon

1. Carbon $\left(\mathrm{C}\right)$ is the element of group 14 and period 2 having the atomic number of 6.
2. The electronic configuration of Carbon $\left(\mathrm{C}\right)$ is $\left[\mathrm{He}\right]2s^{2}2p^2$.
3. As the valence shell of Carbon $\left(\mathrm{C}\right)$ is not completely filled , it needs four electrons to achieve the noble gas configuration and thus Carbon $\left(\mathrm{C}\right)$ forms covalent bond (bond by sharing of electrons).
4. Thus, Carbon $\left(\mathrm{C}\right)$ is reactive element.

Thus, Helium is unreactive element. Therefore, option C is correct.