What effect is created on a round object by gradually changing value?

Correct answer: Smooth volume

Answer: A, smooth volume. A round object turns gradually away from the light, so its surface usually changes from lighter areas through middle values toward darker areas. When an artist represents that transition gradually instead of using an abrupt jump, the eye reads the object as curved and solid. This gradual movement of value is called gradation or modelling in drawing and painting. A is correct because smooth value transitions describe the continuous turning of a rounded surface and create the impression of volume. B is wrong because a value change is about light and dark, not merely about drawing a line. C is wrong because a hard cut suggests an abrupt boundary and is more suitable for a sharp edge or strong separation, not the usual smooth turning of a round object. D is wrong because a colour wheel is a tool or diagram for colour relationships, not the effect created by value gradation. Memory cue: roundness needs a gradual light-to-dark change; abrupt changes make an edge, while gradual changes model volume.