JEE Main 2026 — Jan 23, Shift 2 — Chemistry solution

JEE Main2026Jan 23, Shift 2Chemistry

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 $O^{2 -}$ is larger than that of $F^{-}$ .

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

A
Both statement I and statement II are true
B
Both statement I and statement II are false
C
Statement I is false but statement II is true
D
Statement I is true but statement II is false

Solution

Statement I: After losing one electron, $N a^{+}$ has the noble-gas configuration $1 s^{2} 2 s^{2} 2 p^{6}$ . Removing a second electron means breaking into a stable closed shell, requiring very high energy. For $M g$ , the second electron is removed from the $3 s$ orbital (still a valence shell), giving the stable $M g^{2 +}$ configuration. Hence $I E_{2} (N a) ≫ I E_{2} (M g)$ . True.

Statement II: $O^{2 -}$ and $F^{-}$ are isoelectronic (10 electrons), but $O^{2 -}$ has fewer protons (Z = 8) than $F^{-}$ (Z = 9). Lower nuclear charge means weaker pull on the same electron cloud, so $O^{2 -}$ is larger. True.

Both statements are true.

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