The correct option is B The degree of ionisation decreases.
Presence of other solutes:
When a substance is present in a solution, it may affect the dissociation of another substance.
This is due to common ion effect.
It is the decrease in the degree of ionization of the weak electrolyte, when a strong electrolyte with a common ion is added to the aqueous solution of a weak electrolyte.
For example - For a solution of weak electrolyte CH3COOH :
CH3COOH(aq) + H2O(l)⇌CH3COO−(aq) + H3O+(aq)
when strong electrolyte with common ion CH3COONa is added,
CH3COONa(aq)⇌CH3COO−(aq) + Na+(aq)
According to Le - Chatelier’s Principle,
Reaction goes backward when the concentration of products, (here CH3COO−) increases.
Hence degree of ionization decreases.