Question

why carbon compounds have low melting and boiling point ?

Answer 1

because carbon compounds are made of non metals 
compounds made of non metals are called covalent molecular substances 
covalent molecular substances have low melting and a boiling point because they re weak intermolecular  forces between the molecules of the compound and needs only a little Thermal energy to separate their particles

i think this can hlp u out dear =)

Answer 2

Due to presence of Covalent bonds in Carbon , it has Low melting and Boiling points. Generally , covalent compunds have low boiling and melting point.