Which option is a correct pair of one warm and one cool colour?

Correct answer: Yellow and violet

Colour classification is the governing concept. Yellow is commonly treated as a warm colour, while violet is commonly treated as a cool colour, so option C contains one member of each group. Red-orange and orange-yellow are both warm combinations, and blue-green is generally a cool combination. Although individual hues can shift with context or mixture, the standard school-level colour-wheel classification makes yellow and violet the intended unambiguous answer.