Consider the following graph,

What could be the possible reason for a dip at boron (B) in the above plot?

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Size of boron is smaller than Be

The electron removed during ionisation of boron is a p-electron.

The penetration of a 2s-electron 'is less than that of a 2p-electron

Both (a) and (b)

answer is B.

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Detailed Solution

In boron, the electron removed during ionisation is a p-electron. The 2p-electron of boron is more shielded from the nucleus by inner core of electrons than the 2s electrons. Therefore, it is easier to remove the 2p-electron from boron compared to the removal of a 2s-electron from beryllium. Also, removal of one 2p-electron from boron leads to a comparatively stable configuration of $2 s^{2}$ where the two electrons are paired,

Hence, the first ionization enthalpy of boron (B) is lower than both Be and C.

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