The decreasing order of bond dissociation energies of C−C,C−H and H−H bonds is:
Bond dissociation energies depend on the strength of the bonds. Higher the strength, the greater is the energy.
The bond strength depends upon the extent of overlapping which is dependent on the size of each overlapping atom.
Smaller the size of the atom more will be the bond strength.
Here the size of a hydrogen atom is the smallest but extent of overlapping is more in C−C.
So, the correct order is: C−C>H−H>C−H