Question

Given below are two statements: Statement (I): The radius of isoelectronic species increases in the order. \[ {Mg}^{2+}<{Na}^+<{F}^-<{O}^{2-} \] Statement (II): The magnitude of electron gain enthalpy of halogens decreases in the order. \[ {Cl}>{F}>{Br}>{I} \] In light of the above statements, choose the most appropriate answer from the options given below:

• A. Both Statement I and Statement II are correct.
• B. Statement I is incorrect but Statement II is correct.
• C. Statement I is correct but Statement II is incorrect.
• D. Both Statement I and Statement II are incorrect.

Hint:

When analyzing isoelectronic species, remember that as the nuclear charge increases, the electron cloud is pulled in tighter, decreasing the ionic radius. For electron gain enthalpy, remember that halogens with smaller sizes (like F) have more negative enthalpies due to better electron acceptance.

Answer 1

The Correct Option is C

- Statement I: The radius of isoelectronic species increases as the nuclear charge decreases. So, the correct order is \( {Mg}^{2+}<{Na}^+<{F}^-<{O}^{2-} \), which is correct. 
- Statement II: The magnitude of electron gain enthalpy of halogens increases as the size of the atom increases. The correct order should be \( {Cl}>{Br}>{I}>{F} \), not \( {Cl}>{F}>{Br}>{I} \). Therefore, this statement is incorrect. Thus, the correct answer is that Statement I is correct but Statement II is incorrect.