Final answer:
Graphite is the carbon allotrope that is a major component of pencil lead, known for its slippery feel and electrical conductivity due to its sp²-hybridized carbon atoms and network of resonance structures.
Step-by-step explanation:
The allotrope of carbon that is a black, slippery solid and constitutes a major component of pencil "lead" is graphite. Graphite is composed of layers of carbon atoms arranged in a trigonal planar structure, with each carbon atom connected to three others. The unique properties of graphite, including its electrical conductivity and its softness that allows it to be used as pencil lead, are attributed to its structure where the carbon atoms form sp²-hybrid orbitals and possess resonance forms, facilitating the electrons' movement within the layers.