Question

Which contains the compounds listed correctly in order of increasing boiling points

\(\begin{aligned}{\rm{(a)}}{{\rm{N}}_{\rm{2}}}{\rm{ < C}}{{\rm{S}}_{\rm{2}}}{\rm{ < }}{{\rm{H}}_{\rm{2}}}{\rm{O < KCl}}\\{\rm{(b)}}{{\rm{H}}_{\rm{2}}}{\rm{O < }}{{\rm{N}}_{\rm{2}}}{\rm{ < C}}{{\rm{S}}_{\rm{2}}}{\rm{ < KCl}}\\{\rm{(c)}}{{\rm{N}}_{\rm{2}}}{\rm{ < KCl < C}}{{\rm{S}}_{\rm{2}}}{\rm{ < }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\\{\rm{(d)C}}{{\rm{S}}_{\rm{2}}}{\rm{ < }}{{\rm{N}}_{\rm{2}}}{\rm{ < KCl < }}{{\rm{H}}_{\rm{2}}}{\rm{O}}\\{\rm{(e)KCl < }}{{\rm{H}}_{\rm{2}}}{\rm{O < C}}{{\rm{S}}_{\rm{2}}}{\rm{ < }}{{\rm{N}}_{\rm{2}}}\end{aligned}\)

Short answer

Option (a) is the correct answer.

Step-by-step solution

What is the Boiling point

When the vapour pressure of a liquid is the same as the atmospheric pressure, then the liquid starts to boil. The temperature at this condition is known as the boiling point of that liquid. The stronger the intermolecular force is, the higher will be the boiling point. The intermolecular force existing between polar molecules is much greater than non-polar molecules.

To find the correctly listed order.

Out of given molecules, only KCl and\({{\rm{H}}_{\rm{2}}}{\rm{O}}\) is polar; therefore boiling point of these molecules will be greater than other molecules. Also, since KCl is an ionic compound and ions bonding is expected to be the strongest of all, therefore boiling point of KCl will be greater than \({{\rm{H}}_{\rm{2}}}{\rm{O}}\)

Now, since the molecular weight of \({\rm{C}}{{\rm{S}}_2}\)is greater than \({{\rm{N}}_2}\)therefore boiling point of \({\rm{C}}{{\rm{S}}_2}\) will be greater than \({{\rm{N}}_2}\)

So, correct order is :- \({{\rm{N}}_2}\)<\({\rm{C}}{{\rm{S}}_2}\)<\({{\rm{H}}_2}\)<KCl

Option (a) is the correct answer.