Question

Which from following options is true when an electrolyte solution is diluted ?

• A. both \(\Lambda\) and \(k\) increases
• B. both \(\Lambda\) and \(k\) decreases
• C. \(\Lambda\) increases and \(k\) decreases
• D. \(\Lambda\) decreases and \(k\) increases

Hint:

On dilution, molar conductivity rises but conductivity falls.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Conductivity \(k\) is the conductance of a unit volume of solution. Molar conductivity \(\Lambda_m\) is \(k\) divided by the molarity: \(\Lambda_m = \dfrac{k \times 1000}{M}\).

Step 2: Effect of dilution on k:
When the solution is diluted, the number of ions per unit volume falls. So conductivity \(k\) decreases.

Step 3: Effect of dilution on Lambda:
Concentration falls faster than \(k\) does, and ions also get more freedom to move apart (and weak electrolytes dissociate more). So the ratio \(k/M\) rises, and \(\Lambda_m\) increases.

Step 4: Why the other options are wrong.
Both increasing (A) is impossible since fewer ions per volume lowers \(k\). Both decreasing (B) and \(\Lambda\) decreasing with \(k\) increasing (D) contradict the trend of molar conductivity with dilution.

Final Answer:
On dilution, molar conductivity increases and conductivity decreases. \[ \boxed{\text{(C) }\Lambda\ \text{increases and}\ k\ \text{decreases}} \]