Recall the key definitions

• Conductivity $(\kappa)$ depends on the number of ions present per unit volume.
• Molar conductivity $(\Lambda_m)$ is given by $\Lambda_m = \frac{\kappa \times 1000}{C}$ where $C$ is concentration in $\text{mol L}^{-1}$.

Evaluate each statement

(A) Conductivity always decreases with decrease in concentration for both strong and weak electrolytes.

• On dilution, the number of ions per unit volume decreases.
• Hence, conductivity $\kappa$ decreases for both strong and weak electrolytes.
• So, (A) is correct.

(B) The number of ions per unit volume that carry current in a solution increases on dilution.

• On dilution, volume increases, so ions become more spread out.
• Therefore, the number of ions per unit volume decreases, not increases.
• So, (B) is incorrect.

(C) Molar conductivity increases with decrease in concentration.

• As concentration decreases, interionic interactions reduce.
• Therefore, each mole of electrolyte contributes more effectively to conduction.
• Hence, $\Lambda_m$ increases on dilution for both strong and weak electrolytes.
• So, (C) is correct.

(D) The variation in molar conductivity is different for strong and weak electrolytes.

• For strong electrolytes, $\Lambda_m$ increases only slightly with dilution.
• For weak electrolytes, $\Lambda_m$ increases sharply due to increased dissociation.
• Thus, the variation is indeed different.
• So, (D) is correct.

(E) For weak electrolytes, the change in molar conductivity with dilution is due to decrease in degree of dissociation.

• For weak electrolytes, dilution causes increase in degree of dissociation, not decrease.
• This increase is why molar conductivity rises sharply.
• So, (E) is incorrect.

Count correct statements

Correct statements are: $A,\ C,\ D$

Number of correct statements: $3$

Comparison with stored answer

Stored correct answer = $3$

Our derived answer also = $3$.

Hence, the answer agrees with the stored answer.