The electronic configuration of B and Be is
Be : 1s2, 2s2
B : 1s2, 2s2, 2p1
Here Be has a stable electron configuration, which means that more , energy is required to remove an electron from it. On the other hand, B has one electron in p-orbital.
Since p-orbitals are higher in energy than s-orbital, therefore less stable, it is easier for an electron to be removed from a p-orbital. Electrons located in p-orbitals are farther away from the nucleus, which means that they can withstand its effective nuclear charge better, more easy to remove from the atom.
Losing an electron from its outermost shell will make B more stable, Hence, it will be lower in energy.
