What effect is created by keeping the sky darker at the top and lighter near the bottom?

Correct answer: A sense of distance and openness is created

The governing concept is tonal gradation, in which a gradual change from dark to light suggests atmospheric depth. A darker upper sky and lighter lower area can make the scene feel more spacious and distant, so option B is correct. A smooth transition is important; a flat sky would result from little tonal variation. The effect does not make the whole sky black or remove clouds, because those depend on the actual colours and forms painted.