Which mixture can create red-violet?

Correct answer: More red added to violet

The governing concept is the position of tertiary colours between a secondary colour and a neighbouring primary colour. Violet is made from red and blue; adding more red shifts violet toward red and produces red-violet. Hence option C is correct. Yellow added to green gives yellow-green, yellow added to orange gives yellow-orange, and green added to blue gives blue-green, so none of those mixtures has the required red-violet bias.