Why does tone become darker when spacing between hatching lines is reduced?

Because the visual density of lines increases

Hatching builds tone through the proportion of marks to exposed paper. When the spaces between lines become smaller, more lines occupy the same area and less white paper remains visible. The eye blends this increased mark density into a darker value, so option A is correct. The lines do not automatically become thicker merely because their spacing changes, which makes option C incorrect. Paper reflection is not the governing reason; in fact, reduced visible paper generally reduces the light appearance of the area, so option B is unsuitable. Line direction and cross-hatching can also influence texture and value, but option D is wrong because direction does not become irrelevant. In practice, artists control darkness through spacing, pressure, thickness, and layering.

This is a Class 9 Art Education question. Chapter: Elements of Art. Topic: Line.