Question

The number of alkali metal(s), from Li, K, Cs, $Rb$ having ionization enthalpy greater than $400\, kJ$ $mol ^{-1}$ and forming stable super oxide is

Hint:

Ionization enthalpy and the formation of super oxides are important in determining the chemical behavior of alkali metals.

Answer 1

Correct Answer: 2

The problem involves identifying alkali metals from the provided list that have ionization enthalpies greater than 400 kJ mol^-1 and can form stable superoxides. The alkali metals listed are Li (Lithium), K (Potassium), Cs (Cesium), and Rb (Rubidium).

Step 1: Review Ionization Enthalpies
Lithium (Li): ~520 kJ mol^-1
Potassium (K): ~419 kJ mol^-1
Cesium (Cs): ~376 kJ mol^-1
Rubidium (Rb): ~403 kJ mol^-1
From this, Li, K, and Rb have ionization enthalpies > 400 kJ mol^-1.

Step 2: Formation of Stable Superoxides
Alkali metals form superoxides based on their size and reactivity. Larger alkali metals tend to stabilize the larger superoxide ion (O₂^-). Potassium (K), Rubidium (Rb), and Cesium (Cs) are known to form stable superoxides.

Step 3: Intersection of Conditions
From Step 1: Li, K, and Rb have required ionization enthalpies.
From Step 2: K, Rb, and Cs form stable superoxides.
Therefore, K and Rb satisfy both conditions.

Result: The number of alkali metals meeting both criteria is 2.

This result fits the expected range (2,2).