Question

On descending the alkali metal group, the lattice enthalpies of both the oxide and peroxide (or superoxide) decreased, because:

• A. Radii of the cations increased
• B. Charges on the cations increased
• C. Charges on the cations decreased
• D. It depends on the charges of the oxides

Hint:

Lattice enthalpy is directly related to ion size and charge; a larger ionic radius leads to weaker lattice enthalpy.

Answer 1

The Correct Option is A

Step 1: Lattice Enthalpy.
Lattice enthalpy quantifies the bond strength in ionic solids. It is influenced by ion charges and ionic radii; higher charges and smaller radii lead to greater lattice enthalpy.

Step 2: Alkali Metal Trends.
Moving down the alkali metal group, cation radius grows with added electron shells. This expansion weakens the attraction between cations and anions, thus reducing lattice enthalpy.

Step 3: Conclusion.
Lattice enthalpy diminishes as cation radius increases, aligning with option (1).