UPSC NDA II 2015 General Ability Paper

Concept:The electrical and thermal conductivity of graphite arises because each carbon atom uses $sp^2$ hybridization, forming three sigma bonds and leaving one delocalized electron per atom.Explanation:In graphite, each carbon atom bonds to only three neighboring carbon atoms.This creates a trigonal planar geometry, which corresponds to $sp^2$ hybridization.Each carbon forms three sigma bonds with its neighbours using $sp^2$ hybrid orbitals.The remaining $p_z$ orbital on each carbon overlaps sideways to form a giant delocalized $\pi$ electron cloud.These delocalized electrons can move freely throughout the layered structure.The free movement of electrons allows graphite to conduct heat and electricity efficiently.In contrast, diamond uses $sp^3$ hybridization, with all four valence electrons tied up in strong sigma bonds, leaving no free electrons for conduction.Hence, the correct reason is that each carbon atom in graphite undergoes $sp^2$ hybridization and forms three sigma bonds.Answer:Option A: undergoes $sp^2$ hybridization and forms three sigma bonds with three neighbouring carbon atoms.