Question

Which of the following statements are correct?
LiF is less soluble in water
NaCl is less ionic than CsCl
Formation of alkali metal halide is an endothermic reaction

• A. i & ii only
• B. i, ii & iii
• C. ii & iii only
• D. iii only

Hint:

Solubility and Bond Character.

• LiF: low solubility due to strong ionic lattice.
• NaCl vs CsCl: smaller Na$^+$ polarizes more → more covalent.
• Formation Enthalpies: alkali halides form exothermically.

Answer 1

The Correct Option is A

Option (i) {LiF} is less soluble due to high lattice enthalpy. 
Option (ii) {NaCl} has more covalent character than {CsCl} per Fajan’s rules. 
Option (iii) Formation of alkali halides is exothermic, not endothermic.

Answer 2

Step 1: Understanding the solubility of LiF
LiF (lithium fluoride) is less soluble in water compared to other alkali metal halides because of its very high lattice energy. The strong ionic bonds in LiF require more energy to break apart, making it less soluble despite the hydration energy from water molecules.

Step 2: Comparing ionic character of NaCl and CsCl
NaCl is less ionic than CsCl because the smaller Na⁺ ion has a higher charge density and polarizing power, which distorts the electron cloud of Cl⁻, giving NaCl some covalent character. Cs⁺ is larger and less polarizing, so CsCl behaves more like a purely ionic compound.

Step 3: Formation of alkali metal halides and thermodynamics
The formation of alkali metal halides from their constituent elements is typically an exothermic process, not endothermic. This is because the energy released when the ions form the ionic lattice is greater than the energy required to ionize the metal and dissociate the halogen molecule.

Step 4: Conclusion
Thus, statements i (LiF is less soluble in water) and ii (NaCl is less ionic than CsCl) are correct, while statement iii (formation of alkali metal halide is endothermic) is incorrect.