Question

1st ionisation enthalpy of O is less than N but reverse is true for 2nd.​

Answer 1

Answer:

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Explanation:

It is because oxygen atom is smaller due to a higher effective nuclear charge Zeff=Z−S , where S is approximated to be the number of core electrons and Z is the atomic number. So, it is more difficult to remove the electron from the smaller atom, whose electrons are more tightly bound to the nucleus.