Which tertiary colour is formed when yellow is mixed with orange?

Correct answer: Yellow-orange

The governing concept is the position of tertiary colours on the colour wheel. Yellow is a primary colour and orange is a neighbouring secondary colour, so their mixture is yellow-orange. Option A is correct. Red-orange is made from red and orange, yellow-green from yellow and green, and blue-violet from blue and violet; therefore those distractors use different colour pairs.