Which allotrope of carbon was discovered by Robert F Curl, Harold W Kroto and Richard E Smalley in 1985?

Correct — B. Fullerene is the allotrope Robert Curl, Harold Kroto and Richard Smalley identified in 1985, working on laser-vaporised graphite at Rice University.

The molecule was C60 — sixty carbon atoms closed into a cage of twelve pentagons and twenty hexagons, the pattern of a football. They named it buckminsterfullerene after the architect Buckminster Fuller, whose geodesic domes it resembles.

The three shared the Nobel Prize in Chemistry in 1996 for the discovery, which is option (b).

Why the others are wrong

• (a)
  Lonsdaleite — Lonsdaleite is hexagonal diamond, identified in meteorite material and named after the crystallographer Kathleen Lonsdale. It is not the 1985 discovery.
• (c)
  Carbophene — Carbophene is not the name the 1985 team gave their molecule. What they characterised and named was C60, buckminsterfullerene.
• (d)
  Graphene — Graphene, a single one-atom-thick sheet of graphite, was isolated in 2004 by Andre Geim and Konstantin Novoselov, who took the 2010 Nobel Prize in Physics for it — nearly two decades after the date in the stem.

Allotropes are the same element bonded differently, and carbon's differ dramatically. Diamond ties every atom to four neighbours in a rigid three-dimensional lattice and is the hardest natural material. Graphite stacks flat hexagonal sheets that slide over one another, so it is soft and it conducts.

Fullerenes were the third structural family: closed cages rather than lattices or sheets. C60 is the best known, the family runs on to C70 and larger cages, and the same chemistry opened the way to carbon nanotubes.

Graphene, a single isolated graphite sheet, came nearly two decades later.

Key facts

• Fullerene C60 was discovered in 1985 by Robert Curl, Harold Kroto and Richard Smalley.
• C60 is called buckminsterfullerene, after the geodesic domes of the architect Buckminster Fuller.
• The three shared the Nobel Prize in Chemistry in 1996.
• Graphene was isolated in 2004 by Andre Geim and Konstantin Novoselov, who won the 2010 Nobel Prize in Physics.

Common traps

• Choosing graphene because it is the carbon allotrope most often in the news, when its isolation is dated 2004.
• Treating fullerene as a kind of diamond, when the fullerene cage is a discrete molecule rather than an extended lattice.

No directly related past PYQ was found.