Which colour is formed when more red is added to violet?

Correct answer: Red-violet

The governing concept is hue movement caused by increasing one component in a mixture. Violet shifts toward red when additional red is introduced, creating the tertiary colour red-violet. Option C is therefore correct because red is the dominant direction of the mixture. Blue-green and yellow-green are formed around green, whereas yellow-orange is produced by shifting orange toward yellow, so those distractors do not fit.