Question

why the graphite is smooth and slippery

Answer 1

each carbon in graphite is joined to 3 more carbon

this bond is a weak bond and hence its not a hard substance

Answer 2

the lattice structure of graphite is in such a way that carbon atoms form hexagonal rings and there is free space present between these flat layers..these layers are bounded together by weak forces.....and that's why graphite is smooth and slippery.

hope.it will help.you.