carbon and its compounds
Since electronic configuration of carbon is 1s2 2s2 2p2, thus it has 4 valence elctrons. Hence we can conclude that no other atom small than carbon is present with 4 valence electrons. Thus carbon can form more number of bonds ie 4, and also due to its small size it can form bond with itself, and bonds formed will be more stable, as small size of carbon leads to more overlapping, hence more bond strength. Moreover other elements like silicon,germanium,tin etc with 4 valnces cannot show catenation, as the size if atom is large, lealding to less overlappping and less bond strenght. Although silicon shows catenation too, but not upto that extent.