which one of the following will have higher ionisation enthalpy-
  1. argon and krypton
  2. carbon and nitrogen 

Dear Student,

1. Ionisation energy decreases down the group. This is because as we move down the group, the size of the atom increases and the electron in the last orbital experiences less nuclear force of attraction. Hence, the electron is removed much easily and so the ionisation energy is less. Now, Ar lies above Kr, therefore, Ar has greater ionisation enthalpy than Kr. 

2. Electronic configuration of C= 1s‚Äč2 2s2 2p2
Electronic configuration of N= 1s2 2s2 2p3
If an electron is removes from N, then it will lose its half filled p-orbital stability and will become unstable. Therefore, it is difficult to remove an electron from N.No such thing happen in case of C. Therefore, ionisation energy of N is higher than that of C.

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1. Argon will have higher ionisation enthalpy because ionisation enthalpy decreases down the group. 2. Nitrogen will have higher ionisation enthalpy because of half filled electronic cofiguration. Atoms with half filled have more stability.
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