(b) In graphite, each carbon atom combines with three other carbon atoms with three sigma bonds. So, hybridisation is sp2. In diamond, each carbon atom combines with four other carbon atoms with four sigma bonds. So, hybridisation is sp3. In fullerene, hybridisation of carbon atoms is sp2. Hence, the hybridisation of carbon in graphite, diamond and fullerene, C60 are sp2,sp3 and sp2 respectively.