Which substance is used for making pencil lead?

Concept

Graphite is an allotrope of carbon with atoms arranged in layers.

Weak forces between these layers let thin flakes slide away and leave a dark mark on paper, while clay adjusts the core’s hardness.

Application

A pencil core needs a soft marking material. Graphite has the layered structure and marking behaviour needed for this use, so the named substance used to make pencil lead is graphite.

Contrast

• Sulphur is a brittle non-metal commonly used in sulfuric acid manufacture and rubber vulcanization; those properties do not provide a layered writing medium.

• Silicon is a hard metalloid used chiefly in semiconductors and silicate materials; its structure does not give the soft, transferable flakes needed for ordinary pencil marks.

• The phrase ‘more than one’ would require at least two listed substances to serve as the standard pencil-core material, which the material properties do not support.

• The phrase ‘none of the above’ would apply only if the standard pencil-core material were absent from the list; the material-property comparison resolves that condition.

Cross-check

The dark streak left by a pencil is carbon-based, and changing the graphite-to-clay ratio changes the pencil grade. This independently matches graphite’s role in the core.

Result: Graphite is the correct substance.