Which of the following allotropes of carbon can be used as a lubricant as well as lead in pencils?

Graphite is one of the most common allotropes of carbon. Unlike diamond, graphite is an electrical conductor and can be used, for instance as the material in the electrodes of an electrical arc lamp. Graphite holds the distinction of being the most stable form of carbon under standard conditions. Therefore  it is used in thermochemistry as the standard state for defining the heat of formation of carbon compounds. Pencil cores are called lead, even though they do not  contain lead,  they are typically made of graphite.