Given below are two statements :

Statement (I) : The radii of isoelectronic species increases in the order.

Mg²⁺ < Na⁺ < F^$-$ < O^2-

Statement (II) : The magnitude of electron gain enthalpy of halogen decreases in the order.

Cl > F > Br > I

In the light of the above statements, choose the most appropriate answer from the options given below :

<p>Statement I : Correct</p> <p>The radii of isoelectronic species increases in the order $\mathrm{Mg^{2+} < Na^+ < F^- < O^{2-}}$ (number of electrons = 10)</p> <p>In general, radius of cation is smaller than anion $\mathrm{A^+ < A^-}$ cation with positive charge have higher effective nuclear charge.</p> <p>Reason : In cations, number of electrons decreases, but number of protons remains the same. This causes a stronger pull on the remaining electrons by the nucleus, resulting in a higher effective nuclear charge.</p> <p>With increase in effective nuclear charge, radii decreases so, increase in positive charge indicate more number of electron removal and hence increase in effective nuclear charge. As a result, radii decreases. So, Mg$^{2+}$ has lower radii than Na$^+$.</p> <p>For anion, number of electrons are increased. The electron-electron repulsion weakens the attraction between the nucleus and the electrons, resulting in a decrease in effective nuclear charge. So, effective nuclear charge of O^{2-}$ is lower than F^-$.</p> <p>So, O$^{2-}$ with lower effective nuclear charge causes longer radii of it.</p> <p>So, ${F^ - } < {O^{2 - }}$</p> <p>So, $M{g^{2 + }} < N{a^ + } < {F^ - } < {O^{2 - }}$</p> <p>Ionic radii of isoelectronic species decreases as nuclear charge increases. The cation with greater +ve charge will have a smaller radius and the anion with the greater $-$ve charge will have a bigger radius for isoelectronic species.</p> <p>Statement II : Correct</p> <p>The magnitude of electron gain enthalpy of halogen decreases in the order Cl > F > Br > I.</p> <p>Electron gain enthalpy is the amount of energy released when an atom accepts the electron from any neutral isolated gaseous atom to form an anion.</p> <p>Generally, electron gain enthalpy decreases down the group. The exception is for F and cl. Electron gain enthalpy of F is less than Cl. It is due to the comparatively small size of F atom.</p> <p>For Cl, Br and I, the electron gain enthalpy decreases as go from Cl to I.</p> <p>So, both the statements are correct.</p>