Classification of Elements and Periodicity in Properties - Result Question 31
####31. Correct order of first IP among following elements Be, B, C, N, O is
[2001]
(a) $B<Be<C<O<N$
(b) $B<Be<C<N<O$
(c) $Be<$ B $<$ C $<N<O$ (d)
(d) $Be<B<C<O<N$
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Solution:
- (a) $Be-1 s^{2} 2 s^{2} ; B-1 s^{2} 2 s^{2} 2 p^{1} ; C-1 s^{2} 2 s^{2} 2 p^{2}$; $N-1 s^{2} 2 s^{2} 2 p^{3 ;} O-1 s^{2} 2 s^{2} 2 p^{4}$. 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.
