(a) Graphite is an electrical conductor, but the conductivity is direction dependent. (b) Diamond is more dense than graphite is also correct because of layer structure of graphite. (c) Diamond is meta stable is also correct. It is said to be meta stable, because it is kinetically stable but thermodynamically not stable. (d) Graphite is thermodynamically less stable allotrope is incorrect. Actually graphite is thermodynamically more stable than diamond. Hence, option (d) is the correct answer.