Copper and graphite both conduct electricity at room temperature. Which statement best accounts for the difference in how electrical conductivity arises in these two solids?
a) Copper conducts via σ bonds between metal atoms, whereas graphite conducts via metallic bonding between carbon atoms.
b) In copper, delocalized metallic electrons move freely in three dimensions; in graphite, delocalized π electrons conduct primarily within two-dimensional layers.
c) Both solids conduct because each atom donates exactly one electron to a three-dimensional conduction band that extends throughout the crystal.
d) Copper’s d electrons are localized, limiting conduction to its s electrons along close-packed planes, whereas graphite’s π electrons hop between layers as well as within them, giving three-dimensional conductivity.