Which of the following is NOT an allotrope of carbon?

Trisulfur

The correct answer is option 1. Trisulfur.

Allotropes are different structural forms of the same element, and they can exhibit different physical and chemical properties. In the context of carbon, common allotropes include diamond, graphite, graphene, carbon nanotubes, and fullerenes. However, trisulfur (S₃) is not an allotrope of carbon; it is an allotrope of sulfur.

1. Diamond:

Diamond is a crystalline allotrope of carbon where each carbon atom is tetrahedrally bonded to four other carbon atoms, forming a three-dimensional network. It is known for its hardness and brilliance.

2. Graphite:

Graphite is another carbon allotrope where carbon atoms are arranged in planar hexagonal sheets. It has unique properties, such as lubrication and electrical conductivity along the planes.

3. Lonsdaleite:

Lonsdaleite is a rare hexagonal allotrope of carbon, structurally similar to diamond but with hexagonal symmetry. It is found in some meteorites and is associated with high-pressure conditions.

4. Trisulfur (S₃):

Trisulfur is not an allotrope of carbon; instead, it is an allotrope of sulfur. S₃ molecules consist of three sulfur atoms bonded together in a linear arrangement.

In summary, while diamond, graphite, and lonsdaleite are allotropes of carbon, trisulfur is an allotrope of sulfur. Therefore, the correct answer to the question is option 1. Trisulfur.