The answer to this question would be: b3+
Based on octet rule, atoms tend to give or take electrons by forming an ion until it has eight valence electron.
An atom with valence electron less than 4 will tend to lose the electron and form a cation. Boron is an atom with atomic number 5 which have 3 valence electron. So, Boron should lose 3 of it valence electron and form a +3 cation.
