Why is it incorrect to try making red-orange by mixing red and green?

Correct answer: Green is not one of the secondary colours adjacent to red

Red-orange is a tertiary colour made by mixing the primary colour red with the adjacent secondary colour orange. Green lies opposite red on the traditional colour wheel and is its complementary colour, not its neighbouring secondary colour. Mixing red and green therefore tends to neutralise or muddy the mixture instead of producing red-orange. Option A is correct; red is primary and red-orange is genuinely tertiary.