We know first bond is always sigma bond then is it true that in B2 there is no sigma bond???? Are there Any other exceptions ????

C2's two carbon iotas aren't joined by a twofold bond as normally thought, or even a triple bond, however in actuality a fourfold bond. Two half and half orbitals indicating far from the internuclear area frame the fourth C-C bond. there can be selective pi bonds without coinciding sigma bonds. Some such atoms are B2 and C2.