Given below are two statements:
Statement I : Lithium and Magnesium do not form superoxide
Statement II : The ionic radius of Li⁺ is larger than ionic radius of Mg²⁺
In the light of the above statements, choose the most appropriate answer from the options given below :

Solution

Chemistry ma’am · 4 steps

Tiny Li⁺ and Mg²⁺ pair with the small oxide ion, never the bulky superoxide ion.

1. Check Statement I. When burnt in air, lithium gives the normal oxide Li₂O and magnesium gives MgO. Neither forms a superoxide. Superoxides such as KO₂, RbO₂ and CsO₂ form only with K, Rb and Cs. Statement I is correct.
2. Why no superoxide. A small cation with a high charge density packs best with a small anion such as O²⁻, because that pairing gives the highest lattice energy. The large O₂⁻ ion is stable only alongside large cations of low charge density.
3. Check Statement II. The ionic radius of Li⁺ is about 76 pm and that of Mg²⁺ is about 72 pm. Mg²⁺ has two units of positive charge pulling its electrons in, so it ends up slightly smaller. Statement II is correct.
4. So. Both statements are correct, which is option (c).

The idea to keep. Li and Mg are a diagonal pair with nearly equal ion sizes, so they behave alike: both burn to normal oxides and both form nitrides. Superoxides need big cations like K⁺, Rb⁺, Cs⁺.

Answer from the NTA final answer key. Solution by PrepWiser.