In graphite, a carbon atom is attached with:

The correct option is Three other carbon atoms.

Explanation:

Graphite is an allotrope of carbon with a distinct crystalline structure made up of hexagonal sheets or layers.

1. Hybridization and Bonding:
In graphite, each carbon atom undergoes ${\mathrm{sp}}_2$ hybridization. Out of the four valence electrons of carbon, three are involved in forming strong covalent sigma ($\sigma$) bonds with three neighboring carbon atoms in the same plane. This forms a planar hexagonal network structure.

2. Delocalized Electrons and Conductivity:
The fourth valence electron of each carbon atom remains unhybridized in a $p$-orbital perpendicular to the plane. These unhybridized electrons form a delocalized $\pi$-electron cloud over the layer, which allows graphite to conduct electricity efficiently.

Therefore, each carbon atom in graphite is covalently bonded to three other carbon atoms.