RAS question
Carbon allotropes include all of the following EXCEPT:
Correct answer: (A) Ozone.
Ozone is not a carbon allotrope; it is an allotrope of oxygen, while diamond, graphite and fullerene are allotropes of carbon.
Explanation
Ozone is the exception because it is O3, an allotrope of oxygen, not a form of carbon. NCERT explains that carbon occurs in different natural forms with widely varying physical properties, and specifically lists diamond and graphite as forms made of carbon atoms. Their difference lies in how the carbon atoms are bonded: diamond has each carbon atom bonded to four others in a rigid three-dimensional structure, while graphite has each carbon atom bonded to three others in the same plane, giving a hexagonal arrangement. NCERT also identifies fullerenes as another class of carbon allotropes, with C-60 arranged like a football. The common idea is allotropy: the same element can exist in different structural forms, producing different properties.
Why the other options are wrong
- (B) Diamond is a carbon allotrope because it is formed by carbon atoms bonded in a rigid three-dimensional structure.
- (C) Graphite is a carbon allotrope because it is formed by carbon atoms bonded in planar hexagonal arrangements.
- (D) Fullerene is a carbon allotrope because NCERT identifies fullerenes, including C-60, as another class of carbon allotropes.
Concept
This tests basic chemistry under allotropy and structure-property relationships. It recurs in RAS because questions often ask candidates to separate an element's allotropes from chemically unrelated substances with similar-sounding scientific names.