In which condition will the shading of a sphere look flat?

Correct answer: All parts have the same tone

The governing concept is tonal modelling of a rounded form. A sphere turns continuously away from the light, so its appearance usually needs a gradual shift from the lightest area through middle tones toward the darker side. This continuous value transition helps the viewer read curvature and volume. If every part of the sphere is filled with the same tone, there is no visual evidence of a light-facing side, turning surface, or darker side; the image therefore appears flat. Option C is correct. Option A describes the technique that normally creates roundness, not flatness. Option B places the highlight logically and supports form, while option D can help anchor the sphere to a surface, although it does not by itself create the sphere’s volume. The transition need not be perfectly smooth in every style, but the tonal relationship must communicate turning.