What is the correct way to make bluish violet?

Correct answer: Increase blue

The governing concept is dominance of one component in a mixed colour. Violet is made from red and blue. Increasing the amount of blue shifts the balance toward blue-violet, producing a cooler colour with a stronger bluish appearance; therefore option B is correct. Increasing red would make red-violet, while yellow or green would introduce additional components and could reduce violet’s purity rather than create a clean bluish violet.