Assertion: Boron has a smaller first ionization enthalpy than beryllium. Reason: The penetration of a 2s electron to the nucleus is more than the 2p electron hence 2p electron is more shielded by the inner core of electrons than the 2s electrons.

Electronic configurations of Be and B are 2 2 1 2 s s and 2 2 1 1 2 2 s s p . So, the Outermost subshell of Be is 2s and of B is 2p . Since the penetration power of 2s orbital is more than that of 2p orbital where penetration power is the ability of the orbital for attracting electrons, it is easier to remove the electron from 2p orbital than from 2s orbital. Also, the 2p orbital is well shielded by inner electrons than the 2s orbital. PERIODIC PROPERTIES 64