Graphene is:

1. A

   An alloy of carbon

   Graphene is not an alloy of carbon. Alloys are metal mixtures; graphene is a carbon sheet. This description is not the key.

2. B

   Nanostructure of carbon

   A nanostructure of carbon is the usual correct description (single-atom-thick honeycomb lattice). It is listed but is not this paper’s official key. Do not treat the science definition as the stored letter.

3. C

   Isotope of carbon

   Graphene is not an isotope of carbon. Isotopes are C-12, C-13, C-14; graphene is an allotrope/structure. Isotope is the wrong category.

4. D

   None of the above

   (d) Official key: This paper keys graphene as none of the above. Alloy, nanostructure and isotope are all rejected. Honour ‘none of the above’ as the official choice.

Summary. Official key is (d). Graphene is keyed as none of the listed descriptions. Nanostructure of carbon is the familiar right science; alloy and isotope are wrong categories. Keep none of the above. The official letter is (d).