When yellow is added to red-orange in which direction will the mixture generally move?

Correct answer: Toward yellow-orange

Colour mixing shifts a hue toward the colour that is added, although the exact result depends on pigment proportions. Red-orange already lies between red and orange; adding yellow moves it toward the yellow side of orange, namely yellow-orange. Blue-green and blue-violet are on the cool side, while red-violet moves toward violet, so option A is correct.