Question

Correct order of volatility is

$${\mathbf{A}}.\;\;{\mathbf{HF}} > {\mathbf{HCl}} > {\mathbf{HBr}} > {\mathbf{HI}} \\\ {\mathbf{B}}.\;\;{\mathbf{HCl}} > {\mathbf{HBr}} > {\mathbf{HI}} > {\mathbf{HF}} \\\ {\mathbf{C}}.\;\;{\mathbf{HI}} > {\mathbf{HBr}} > {\mathbf{HCl}} > {\mathbf{HF}} \\\ {\mathbf{D}}.\;\;{\mathbf{HBr}} < {\mathbf{HCl}} < {\mathbf{HI}} < {\mathbf{HF}} \\\$$

Answer 1

The volatility of compound is its characteristic feature to have more vapor pressure at normal temperature. Van der Waals forces are existent in between of all molecules, but when the molecules are small they are the weakest forces.

Complete step-by-step answer: The correct answer to the question is $HCl > HBr > HI > HF.$
Volatility is governed by the intermolecular forces of a compound. Molecular weight increases with increase in the Van der Waal forces. So, the predictable order has to be: $HF < HCl < HBr < HI$. But we must keep this in mind that $HF$ is having hydrogen bonding and the scope of Hydrogen bonding is very high due to high electronegativity of fluorine as well as the linear bonding. Volatile substance means one that easily evaporates in the atmosphere. It is easy to break bonds amidst hydrogen and fluorine for the reason that the interatomic distance between the two is very large and also that fluorine is self-stabilizing due to its atomic size. The negative charge of fluorine will extend all over the atom. For that reason, $HF$ is the least volatile.
As we saw earlier that $HF$ because of hydrogen bonding is least volatile. Since the molecular weight increases the intermolecular forces also increase owing to which Van der Waal forces of attraction also increase. Accordingly $HCl$ is a gas and HI is a liquid.

Note: The more volatile a substance is, the easier it is to do the process of evaporation. Liquids get converted to vapour at all temperatures, since the Maxwell-Boltzmann energy distribution curve says that there are always some particles having sufficient energy to get out of the body of liquid. We should keep in mind that the intensification of a charge of the compound makes it unstable.