Given below are two statements : Statement I : The second ionisation enthalpy of Na is larger than the corresponding ionisation enthalpy of Mg. Statement II : The ionic radius of O²⁻ is larger than that of F⁻. In the light of the above statements, choose the correct answer from the options given below.

Second ionisation enthalpy of Na and Mg and ionic radius of O2− and F−

Q. Given below are two statements :

Statement I : The second ionisation enthalpy of Na is larger than the corresponding ionisation enthalpy of Mg.

Statement II : The ionic radius of O²⁻ is larger than that of F⁻.

In the light of the above statements, choose the correct answer from the options given below

A. Statement I is true but Statement II is false

B. Statement I is false but Statement II is true

C. Both Statement I and Statement II are true

D. Both Statement I and Statement II are false

Correct Answer: Both Statement I and Statement II are true

Explanation

Statement I:
Electronic configuration of Na is:

$$ \mathrm{Na : 1s^2 2s^2 2p^6 3s^1} $$

After loss of one electron, Na⁺ attains noble gas configuration:

$$ \mathrm{Na^+ : 1s^2 2s^2 2p^6} $$

Removal of second electron from Na⁺ requires breaking a stable noble gas configuration, hence second ionisation enthalpy of Na is very high.

For Mg:

$$ \mathrm{Mg : 1s^2 2s^2 2p^6 3s^2} $$

Second ionisation of Mg removes a 3s electron and does not disturb noble gas configuration. Therefore, second ionisation enthalpy of Na is greater than that of Mg.

So, Statement I is true.

Statement II:
O²⁻ and F⁻ are isoelectronic species (10 electrons each).

In isoelectronic species, ionic radius decreases with increase in nuclear charge.

O has atomic number 8, while F has atomic number 9. Hence, O²⁻ has lower nuclear charge and larger ionic radius compared to F⁻.

So, Statement II is also true.

Therefore, both Statement I and Statement II are true.

Explanation

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