The correct answer is option 3: Carbon (Graphite).

Pencil leads are not made up of lead, as the widely used term "pencil lead" may suggest. Instead, pencil leads are made up of a form of carbon called graphite. Graphite is a naturally occurring mineral that is composed of carbon atoms. It is mined and processed into the form of thin cylindrical rods that are then inserted into wooden pencils.

While lead is a commonly known element, it is not used in pencil leads due to its toxicity. In the past, however, pencils were made with lead, but this practice was phased out when it was discovered that lead can be harmful if ingested or if graphite dust containing lead is inhaled.

Zinc and tin are not used in pencil leads as they have different properties and are not suitable for creating the dark markings necessary for writing or drawing. Therefore, option 1 (Zinc) and option 4 (Tin) are incorrect.

In conclusion, the correct element used in pencil leads is carbon in the form of graphite.