Question

Which of the following compounds are covalent
A) Hydrogen gas
B) Calcium oxide
C) Potassium chloride
D) Sodium sulfide

Answer 1

Hint: The metals usually form ionic bonds as they can remove their electrons easily. Whereas the non metals form covalent bonds by sharing electrons among them.

Complete step by step solution:Potassium chloride has the molecular formula of $KCl$ . Here potassium has one electron and chlorine has seven electrons in its valence shell. Potassium is a metal. So, it removes its electron and chlorine accepts the electron. Thus ionic bonds are formed.
Calcium oxide has the molecular formula of $CaO$ . Here calcium has two electrons and oxygen has six electrons in its valence shell. Calcium is a metal. So, it removes its electron and oxygen accepts the electron. Thus ionic bonds are formed.
Sodium sulfide has the molecular formula of $N{{a}_{2}}S$ . Here sodium has one electron and sulfur has six electrons in its valence shell. sodium is a metal. So, it removes its electron and sulfur accepts the electron. Thus ionic bonds are formed.
The general valence shell electronic configuration of hydrogen atom is $1{{s}^{1}}$.

Thus it contains one more electron in the ns subshell. Thus it needs one electron to get the noble gas configuration and become stable. Thus two hydrogen atoms come close and share their electrons to form a covalent bond.

Thus the correct option is A.

Note: The covalent bond present in hydrogen is non polar in nature as the two atoms are the same. Thus there is no charge separation between the hydrogen atoms and it is highly stable.