Which mixture creates red-orange?

Correct answer: Red and orange

The governing concept is the formation of tertiary hues from adjacent colours. Red-orange lies between red and orange on the colour wheel, so it is made by mixing red, a primary colour, with orange, a neighbouring secondary colour. Therefore option C is correct. Red and blue produce violet, yellow and green produce yellow-green, and blue and green produce blue-green, so the other pairs name different results.