The percentage is 0%. "Lead" in this case is a misnomer. Pencil "Lead" is made of graphite (an allotrope of carbon) and different levels of clay to control hardness.
Pencils have never contained the metal, lead, although the word commonly used to describe the centre core of a pencil is, in English, 'lead'. The ancient tool which preceded the modern pencil was a...
Graphite is present in pencil leads. it is composed of carbon atoms covalently bonded with each other, and 1 free valence electron in each atom (which explains why graphite/pencil-lead conducts...