QAIPM-2001-Ch-2865: NEET 2001 Chemistry - Class 11 AIPM-2001-Ch-2865 Solution: Correct order of 1st ionization potential among following…

Be � 1s 2 2s 2 ; B � 1s 2 2s 2 2p 1 ; C � 1s 2 2s 2 2p 2 ; N � 1s 2 2s 2 2p 3 ; O � 1s 2 2s 2 2p 4 . IP increases along the period. But IP of Be > B. Further IP of O < N because atoms with fully or partly filled orbitals are most stable and hence have high ionisation energy. As in case of boron, 2p 1 electron have to be removed to get B + (1s 2 2s 2 ) from B(1s 2 2s 2 2p 1 ), while in case of Be (1s 2 2s 2 ) electron have to be removed to get Be + (1s 2 2s 1 ). p electron can be removed more easily than s electron so the energy required to remove electron will be less in case of boron.