Electronic configuration of Be =1s22s2
Electronic configuration of B =1s22s22p1
Due to full-filled configuration of Beryllium, it has higher first ionization energy.
Effective nuclear charge
Zeff of Be =4−σ=4−(2×0.85+0.35×1)=2.05
Zeff of B =5−σ=5−(2×0.85+0.35×2)=2.6
∴Zeff of B > Zeff of Be