Molar conductivity increases with.....

Decrease in concentration

The correct answer is Option (3) → Decrease in concentration

Molar conductivity (Λm) = Conductivity / Molar concentration

It depends on:

• Number of ions available
• Mobility of ions

On dilution, ions move more freely and inter-ionic attraction decreases → Λm increases.

Option-wise Explanation

1. Increase in concentration

When concentration increases, ions come closer together. Inter-ionic attraction and ion-ion collisions increase. This reduces the mobility of ions. Even though the number of ions per volume is more, their movement becomes restricted. Therefore, molar conductivity actually decreases.

2. Increase in pressure

Pressure has almost no significant effect on molar conductivity of liquid solutions. Liquids are nearly incompressible, so ion mobility and ion separation remain almost unchanged. Hence, molar conductivity does not increase appreciably with pressure.

3. Decrease in concentration

Correct. On dilution, ions are farther apart. Inter-ionic attraction decreases and ions move more freely. In weak electrolytes, degree of ionization also increases. Both effects increase the number of effective charge carriers and their mobility, so molar conductivity increases.

4. Decrease in pressure

Reducing pressure does not significantly change the volume or ion movement in liquids. Therefore, molar conductivity remains almost unaffected. This is not the main factor controlling molar conductivity.