Correct Answer – B
(a) Diamond is harder than graphite. Hence (a) is incorrect.
(b) Graphite is a good conductor of electricity at eacj C-atom is attached to three other C-atoms and 4th electron is free while in diamond, all the four valenies are satisfied and hence, it is insulator. Thus (b) is correct.
(c) Diamond, is better thermal conductor than graphite . This is because thermal conduction is due to transfer of thermal vibrations from atom to atom which is easier in a compact crystal like that of diamond. Hence, (c) is incorrect.
(d) In graphite, C-C bond acquires some double bond character. Hence, it has higher bond order than diamond . Thus (d) is incorrect.