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

The electronic confugration of
Boron: 1s2 2s2 2p1
&
Beryllium: 1s2 2s2 are given . so we see that
Beryllium has two electrons in its outermost orbital which is 2s orbital. The electrons in the 2s orbital are already paired and hence it is quite a stable configuration for the beryllium atom. Hence the first ionization enthalpy of beryllium is higher than that for boron. However, if one would consider the second ionization enthalpy of beryllium and boron, the one for boron would be higher as after the removal of first electron of Boron from 2p1 orbital, the next electron would be in the 2s orbital, where it would be already paired with another electron and removing it would be more difficult.

Answer 2

because it is because ionisation enthalpy depends on the sum on sublimation and hydration enthalpy. so, beryllium has the greater sum of the sublimation and hydration enthalpy as compared to Boron due presence of only 2 electrons while in case of Boron it is divided into 3 ionization enthalpy due to presrnce of three electrons in its outermost shell. therefore the first ionization enthalpy of beryllium is greater than the Boron.
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