Question

Which of the following is most volatile?
A. $${{\text{H}}_{\text{2}}}{\text{O}}$$
B. $${{\text{H}}_{\text{2}}}{\text{S}}$$
C. $${{\text{H}}_{\text{2}}}{\text{Se}}$$
D. $${{\text{H}}_{\text{2}}}{\text{Te}}$$

Answer 1

Hint: The volatility property of substance is defined as its tendency to evaporate or vaporise. It has a measurable vapour pressure. It is the tendency of the molecules to escape from the molecule. The substance which gets easily and quickly escaped from the molecule is more volatile.

Complete step by step answer:
The volatility depends upon the interactions present between the molecules. If the attraction between the atoms or molecules of the substance is more then it will be attracted towards each other and bonded tightly and will not be able to evaporate easily. So the bond length between the atoms also matters in the volatility. If they have less bond length that means they are closely attached to each other so the volatility will be less. In this case the water molecule has hydrogen bonding so it will be least volatile due to strong bonding but the rest have Vander waals force of attraction. These are the hydrides of group 16 and we know that the electronegativity decreases down the group. As down the group the atom size increases so the Vander waals force of attraction increases so the volatility decreases. The last element is Te in group 16. So the most volatile is $${{\text{H}}_{\text{2}}}{\text{Te}}$$.

So, the correct answer is Option D.

Note: The volatility is directly proportional to the bond length and atomic size. As the size increases the nucleus and outermost electron attraction decreases so the electron is able to remove easily. The other factor is the nature of bonding as hydrogen bonding is strong so molecules will not escape but in van der waals forces there are chances to escape.