Which option shows a correct pair of a primary colour and its adjacent secondary colour?

Correct answer: Red and orange

In the traditional colour wheel, red is a primary colour and orange is the adjacent secondary colour formed from red and yellow. Their neighbouring relationship produces the tertiary hue red-orange, so option A is correct. Red and green, yellow and violet, and blue and orange are complementary or non-adjacent relationships, not the required primary-adjacent-secondary pair.