Why ionization enthalpy of berylium is more than that of boron ?

Explanation

Ionisation enthalpy of Be and B can be explained on the basis of their electronic configurations. The electronic configurations of Be and B are as follows:
`Be(Z=4)=1s^(2)2s^(2),B(Z=5)=1s^(2)2s^(2)2p^(1)`
From here, Be has fully filled s-orbital whereas B has incompletely filled p-orbital. So, this fully filled configuration makes Be more stable than B.
Secondly, s-electrons are more closer towards the nucleus. Therefore, s-electrons of Be show more penetration towards the nucleus. Thus, the more the penetration effect, the more will be the ionization enthalpy. Hence, Be has more ionization enthalpy than the B.