Which of the following statements are correct?
(A) Both LiCl and MgCl₂ are soluble in ethanol.
(B) The oxides Li₂O and MgO combine with excess of oxygen to give superoxide.
(C) LiF is less soluble in water than other alkali metal fluorides.
(D) Li₂O is more soluble in water than other alkali metal oxides.
Choose the most appropriate answer from the options given below :

Solution

Chemistry ma’am · 2 steps

Lithium copies magnesium, so test each statement against what Mg does, not what Na or K do.

1. Why Li behaves differently. Li⁺ is very small and highly polarising. This makes its compounds more covalent and gives them high lattice enthalpies. In these ways lithium resembles magnesium (the diagonal relationship), not the other alkali metals.

   Statement	Verdict	Reason
   (A) LiCl, MgCl₂ soluble in ethanol	Correct	Small, polarising cations give these chlorides covalent character, so both dissolve in organic solvents like ethanol.
   (B) Li₂O, MgO form superoxides	Wrong	Li and Mg give only normal oxides. Their small cations cannot stabilise large peroxide or superoxide ions, so no superoxide forms.
   (C) LiF least soluble fluoride	Correct	Small Li⁺ with small F⁻ gives a very high lattice enthalpy, which hydration cannot overcome.
   (D) Li₂O most soluble oxide	Wrong	Small Li⁺ with small O²⁻ again means a very high lattice enthalpy, so Li₂O is the least soluble alkali metal oxide.

2. So. Only (A) and (C) are correct, which is option (a).

The idea to keep. A small Li⁺ with a small anion means a high lattice enthalpy and low water solubility. Small cations also cannot stabilise big anions like superoxide.

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