Which colour group creates a calm and cool effect?

Correct answer: Blue green purple

Cool colours are commonly associated with blue, green, and violet or purple. They may suggest water, sky, shade, distance, freshness, and quietness, so artists often use them to create a calm or cool mood. The emotional effect is not an unchangeable rule, but it is a standard principle taught in basic colour theory. Red, yellow, and orange are generally classified as warm colours instead.

Among the choices, option D contains blue, green, and purple. The other groups contain warm colours such as red, yellow, or orange, with black added in one group. Since the question asks for the group that creates a calm and cool effect, option D follows directly from the cool-colour classification.