In which of the following arrangements the order is NOT according to the property indicated against it?
In which of the following arrangements the order is NOT according to the property indicated against it?
(a) Al3+ < Mg2+ < Na+ < F increasing ionic size
(b) B < C < N < O increasing first ionisation enthalpy
(c) I < Br < F < Cl increasing electron gain enthalpy (with negative sign)
(d) Li < Na < K < Rb increasing metallic radius
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(b) : As we move from left to right across a period, ionisation enthalpy increases with increasing atomic number. So the order of increasing ionisation enthalpy should be B < C < N < O.
But N(1s2 2s2 2p3 ) has a stable half filled electronic configuration. So, ionization enthalpy of nitrogen is greater than oxygen.
So, the correct order of increasing the first ionization enthalpy is B < C < O < N.
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