Atomic no. of Boron(B) is 5. Electronic configuration of B= 1s²2s²2p¹. Due to small size of atom (B) and extra STABILITY of fully filled orbital i.e.(B+ =1s²2s²) a very large AMOUNT of energy is REQUIRED to remove 2 more electrons from 2s orbital which is practically not possible.therefore B+3 does not exist and B+ therefore exist.