In case of the following questions, a statement I is given followed by a corresponding statement II just below it. Mark the correct answer.

Statement I: Ammonium chloride dissolved in water results in cooling of solution.

Statement II: Reaction is endothermic.

If both statement I and statement II are true and statement II is the correct explanation of statement I

The correct answer is option 1. If both statement I and statement II are true and statement II is the correct explanation of statement I.

Let us delve into the explanation for each statement and how they relate to each other:

Statement I: Ammonium chloride dissolved in water results in cooling of solution.

This statement is true. When ammonium chloride (\(NH_4Cl\)) is added to water, it dissolves and dissociates into ammonium ions (\(NH_4^+\)) and chloride ions (\(Cl^-\)):

\(NH_4Cl (s) \rightarrow NH_4^+ (aq) + Cl^- (aq)\)

For this dissolution process, the system absorbs heat from the surrounding water. As a result, the temperature of the water decreases, leading to the observed cooling effect.

Statement II: Reaction is endothermic.

This statement is also true. A reaction is defined as endothermic if it absorbs heat from its surroundings. During the dissolution of ammonium chloride in water, the process requires energy to overcome the lattice energy of the solid and to solvate the ions in water. This energy comes from the thermal energy of the water, resulting in a decrease in the temperature of the solution.

Dissolution Process:

Lattice Energy: This is the energy required to separate the ions in the solid ammonium chloride. In the solid state, \(NH_4^+\) and \(Cl^-\) ions are held together by strong ionic bonds, forming a lattice structure. Breaking these bonds requires energy input, which is provided by the surrounding water in the dissolution process.

Hydration Energy: When the \(NH_4^+\) and \(Cl^-\) ions enter the aqueous phase, they interact with water molecules. The water molecules surround the ions, stabilizing them through ion-dipole interactions. This process releases energy, known as hydration energy.

Net Energy Change: The overall enthalpy change (\(\Delta H\)) of the dissolution process is determined by the balance between the energy absorbed to break the ionic bonds (lattice energy) and the energy released during the hydration of ions. For ammonium chloride, the lattice energy is higher than the hydration energy released, resulting in a net absorption of energy from the water, making the process endothermic.

Relationship Between Statements:

Cooling Effect (Statement I): The observed cooling is due to the endothermic nature of the dissolution process. As ammonium chloride dissolves, it absorbs heat from the water, leading to a decrease in the temperature of the solution.

Endothermic Reaction (Statement II): This provides the explanation for why the solution cools. Since the dissolution is endothermic, it requires heat absorption from the surroundings (the water), causing the temperature to drop.

Conclusion:Both statements are true:

Statement I correctly describes the cooling effect observed when ammonium chloride dissolves in water. Statement II correctly identifies the dissolution process as endothermic, which explains why the cooling occurs.

Therefore, the correct answer is: 1. If both statement I and statement II are true and statement II is the correct explanation of statement I.