Assertion (A): Molar conductivity of $\text{0}{\text{.1 M NH}}_{\text{4}}\text{OH}$ solution is less than that of $\text{0}{\text{.001 M NH}}_{\text{4}}\text{OH}$ solution.

Reason (R) : Dilution increases the degree of ionisation of ${\text{NH}}_{\text{4}}\text{OH}\text{.}$

Assertion and Reason Explanation

Assertion (A): The molar conductivity (Λ_m) of 0.1 M NH₄OH solution is less than that of 0.001 M NH₄OH solution.

This occurs because molar conductivity increases with dilution for weak electrolytes like NH₄OH. At lower concentration (higher dilution), the ions are more separated, and the degree of ionisation increases, leading to higher molar conductivity.

Reason (R): Dilution increases the degree of ionisation of NH₄OH.

Weak electrolytes ionise more as they are diluted. Greater ionisation means more ions are available to carry the current, directly increasing molar conductivity.

Λ_m = ^{K × 1000}⁄_M

As molarity (M) decreases (solution is diluted), molar conductivity increases. This is because:

Λ_m ∝ V given that M = n / V, where n is the number of moles and V is volume.

Therefore, 0.001 M NH₄OH has higher molar conductivity than 0.1 M, due to increased ionisation with dilution.

Both assertion and reason are true, and the reason correctly explains the assertion.