Question

Although B (Boron) is smaller in size as compared to Be (Berellium) but the first ionisation enthalpy of Be (Berellium) is higher than B (Boron).

Answer 1

Although Boron is smaller in size than Be. But 1st ionization of Be is greater than B for the following reasons:
Ionization energy means energy required to remove an electron from neutral gaseous atom.
Electronic configuration of Beryllium is 1S2 2S2(since the orbitals are filled completely, its going to be become stable and when atom is stable its very hard to remove electron from it.
Where as B electronic configuration Is 1s2 2s22p1(since the last p orbital is not filled completely then its going to stay unstable and also the energy of P orbital is higher than S orbital so it will be easy to remove an electron from it.
Hope this helps you !!