Conductivity of a solution is directly proportional to:

The essential feature of electrolytes is conductivity.

It is a measurement of an aqueous solution's ability to conduct electricity.

Because the degree of dissociation increases while the number of ions per unit volume drops, the conductivity of the electrolyte solution reduces when it is diluted.

Dilution has an inverse relationship with conductivity.

The number of ions per unit volume is directly proportional to conductivity.

The quantity of current flowing through a unit cross-sectional area is known as current density.

The current density has no effect on conductivity.

The quantity of ions per unit volume reduces as the volume increases.

As a result, conductivity and volume are inversely proportional.

Hence, the correct option is B, i.e. Number of ions.