The correct option is D Nature of solvent
Theory:
Factors affecting degree of Ionization:
1. Nature of electrolyte: Weak electrolyte dissociates less and strong electrolyte dissociates more
2. Nature of the solvent: The ionizing power of the solvent depends upon its dielectric constant. Greater the value of dielectric constant greater will ionizing power of solvent and greater will be the degree of ionization. For example, water has a high dielectric constant and it is generally taken as a solvent.
3. Temperature: Effects K value as (Kw∝T)
4. Dilution: On dilution α value increases. More the dilution , more is the ionisation.
(α=1 at infinte dilution)
5.Presence of other solutes: When a substance is present in a solution, It may affect the dissociation of another substance. This is due to the common ion effect.