MCQ Detailed View

Hydrogen bonding is a type of intermolecular force that arises when a hydrogen atom covalently bonded to a highly electronegative atom such as oxygen, nitrogen, or fluorine interacts with the lone pair of electrons on another electronegative atom. This special interaction is responsible for many unique physical and chemical properties of compounds.

In water (H₂O), hydrogen bonding is extremely strong and extensive. Each water molecule can form up to four hydrogen bonds, two through its hydrogen atoms and two through the lone pairs of oxygen. This network of hydrogen bonds is the reason water has an unusually high boiling point, high specific heat, high surface tension, and expands on freezing.

In ethyl alcohol (C₂H₅OH), the hydroxyl group (–OH) is capable of forming hydrogen bonds. These bonds exist between the hydrogen of one alcohol molecule and the oxygen of another. Due to hydrogen bonding, alcohols have higher boiling points compared to ethers or hydrocarbons of similar molecular weight. Hydrogen bonding also plays a role in alcohol solubility in water.

In phenol (C₆H₅OH), hydrogen bonding can occur in two ways. Intermolecular hydrogen bonding exists between the –OH groups of different phenol molecules. Intramolecular hydrogen bonding can also occur in substituted phenols where the hydroxyl group interacts with nearby substituents on the aromatic ring. The presence of hydrogen bonding influences the physical state, boiling point, and solubility of phenol in water.

Therefore, water, ethyl alcohol, and phenol all show hydrogen bonding. This makes “All of these” the correct answer. The concept of hydrogen bonding is fundamental in understanding the properties of not only small molecules but also large biomolecules like proteins and DNA, where hydrogen bonds stabilize secondary and tertiary structures.