The molecule which the highest boiling point is: (a) \(\mathrm{CH}_{3}-\mathrm{CHCl}-\mathrm{CH}_{3}\) (b) \(\mathrm{CH}_{3}-\mathrm{CHOH}-\mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{Cl}\) (d) \(\mathrm{CH}_{3}-\mathrm{CHOH}-\mathrm{CH}_{3}\)

Imagine molecules as tiny particles not just floating in space, but interacting with each other with invisible hands known as intermolecular forces. These forces play a crucial role in determining a molecule's physical properties, including its boiling point.

There are several types of intermolecular forces, with London dispersion forces being the most common and weakest, present in all molecules. They arise due to temporary shifts in the electron cloud surrounding molecules. On the other hand, dipole-dipole interactions are a bit stronger and occur between molecules with permanent dipoles – think of them as magnets pulling each other with their opposite charges.

The strongest of these 'invisible hands' are hydrogen bonds, which are special dipole-dipole interactions that occur when hydrogen is attached to highly electronegative elements such as oxygen, nitrogen, or fluorine. These bonds can affect the physical properties of a substance significantly.

Hydrogen bonding is the superstar when it comes to intermolecular attractions. It's like a special handshake that only a few can perform, and it has a significant impact on the boiling points of molecules.

These bonds occur when a hydrogen atom is directly bonded to an electronegative atom, and this duo gets attracted to another electronegative atom nearby. The result is a strong, though not covalent bond that can dramatically increase a substance's boiling point.

In the context of the exercise, molecules with –OH groups, like option (b) with two hydroxyl groups, can create multiple hydrogen bonds with other molecules, leading to higher boiling points. This is because hydroxyl groups are both hydrogen donors and acceptors, making for a highly interactive molecular dance that requires more energy, in the form of heat, to break apart.

Understanding the physical properties of molecules is like getting to know someone's personality. Boiling point, one of these properties, is influenced by the molecule's intermolecular forces. It's a temperature at which a liquid becomes a gas, a real-life drama where molecules must overcome their attractions to each other to break free and vaporize.

The more hydrogen bonds a molecule can form, the higher the temperature it needs to reach to boil. This is the case with molecule (b) in our exercise. Its dual hydroxyl groups enable extensive hydrogen bonding, leading to a higher boiling point compared to its classmates. On a microscopic level, it's like a tight group hug that's harder to break, requiring more energy to do so.

The physical properties stemming from these molecular interactions not only tell us about boiling points but also hint at solubility, viscosity, and surface tension among other characteristics. They define the behavior of substances in different environments, which is of paramount importance in many scientific and industrial applications.