Question

Statement-1: The boiling point of ${C_2}{H_5}OH$ is less than that of ${H_2}O$ though the molecular weight of ${C_2}{H_5}OH$ is more than that of water.
Statement-2: ${C_2}{H_5}OH$ molecules are not highly associated through hydrogen bonding as in water.
A. Statement-1 is True, Statement-2 is True; Statement-2 is a correct explanation for Statement-1.
B. Statement-1 is True, Statement-2 is True; Statement-2 is NOT a correct explanation for Statement-1.
C. Statement-1 is True, Statement-2 is False.
D. Statement-1 is False, Statement-2 is True.

Answer 1

Hint: One statement compares the boiling point of ${C_2}{H_5}OH$ and ${H_2}O$; another statement explains the hydrogen bonding present in these compounds. Hydrogen bonding is a dipole-dipole attraction between molecules containing hydrogen. Due to hydrogen bonding, hydrogen atoms develop a good amount of positive charge. The more the positive charges of hydrogen, the stronger the hydrogen bonding will be.

Complete step by step solution:
Hydrogen bonding is just an attraction not a bond. It happens between a hydrogen atom and a very electronegative atom; hydrogen must be bonded to another very electronegative atom. It occurs between two different molecules.
In water molecules (${H_2}O$), oxygen atoms have two lone pairs of electrons left after covalent bonding. Two hydrogen atoms are bonded to single oxygen in water. Due to the hydrogen bonding between oxygen of one water molecule with hydrogen of another water molecule, hydrogen develops a positive charge and oxygen develops a negative charge. Hydrogen will be strongly attached to this oxygen, and the attraction will be stronger than an ordinary dipole-dipole interaction.
In ethanol (${C_2}{H_5}OH$), also known as ethyl alcohol, we have a hydroxyl group and only one hydrogen is attached to an oxygen atom, oxygen has two lone pairs. This oxygen atom is hydrogen bonded with the hydrogen atom of another ethanol molecule. Here also, there will be a development of charges for oxygen and hydrogen, but the attractions between oxygen and hydrogen are not as strong as they are in water molecules. Because ethanol develops only one positive charge and water develops two positive charges. And two lone pairs of oxygen are balanced by hydrogen bonding with other two hydrogens in water whereas it is not completely in ethanol.
Thus it takes more heat to break the attractions in water than in ethanol.So the boiling point of water is greater than that of ethanol irrespective of their molecular weights.
Both the statements are correct and statement-2 is a correct explanation of statement-1.

The correct option is Option A.

Note:
Assertion means a statement and reason is the explanation about that particular statement. Here statement 1 is the assertion and statement 2 is the reason. You have to find out whether each statement is correct or not. If both the statements are correct, you have to find out whether the reason supports the assertion or not. Do not confuse in answering these types of questions. All Hydrogen bondings are dipole-dipole attractions but not vice-versa.