Question

$HCl$ gas is covalent and $NaCl$ is an ionic compound. This is because:
A. Sodium is highly electropositive
B. Hydrogen is a non-metal
C. $HCl$ is a gas
D. Electronegativity difference between $H$ and $Cl$ is less than 2.1

Answer 1

Hint: The reason can be found out by the tendency of an atom to attract a shared pair of electrons towards itself. This tendency depends on the atomic number and the distance at which valence electrons reside from the charged nucleus. Scientist Pauling discovered a scale for measuring this value of the tendency of the atom.

Complete step by step answer:
The tendency of the atom to exhibit such property is called electronegativity.
If the electronegativity difference is lesser, then it tends to be a covalent compound. And if the electronegativity difference is higher, then it used to be an ionic compound.
As per Pauling scale, electronegativity value of hydrogen is considered to be the standard one that is 2.1.
In case of $HCl$ gas, electronegativity difference is less than 2.1 (electronegativity value of $H$ is 2.1 and that of $Cl$ is 3.0). So it tends to exist as a covalent compound.
Whereas in case of $NaCl$, electronegativity difference is more than 2.1 (electronegativity value of $Na$ is 0.9 and that of $Cl$ is 3.0). So it tends to exist as an ionic compound.
So, the correct option is D.

Note: Across a period in the periodic table from left to right, electronegativity value increases and across a group from top to bottom, the value decreases. Fluorine is the most electronegative element and Francium is the most electropositive element.