Atomic no of Be is 4 so its electronic configuration is 2,2
or Is2 2s2 which is similar to Noble gas configuration( 2
e in outermost shell as that of He). Hence it is difficult to remove electron
from it and require more energy.
Atomic no of B is 5 so its electronic configuration is 2,5
or 1s2 2s2 2p1 which is likely to loose 1 electron
to get He configuration. Hence welcome the removal of electron which need less
energy compared to Be.