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

JEE Main · 2023 · 31 Jan 2023 · Shift 2 · s-Block Elements

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 ____.

Answer: 2

Stable superoxides of the type

M O_{2}

are formed only by the larger alkali metals potassium, rubidium and caesium. Their first ionization enthalpies are about

419

403

and

376 kJ mo l^{- 1}

respectively, so of the superoxide formers only potassium and rubidium exceed

400 kJ mo l^{- 1}

. The number of alkali metals meeting both conditions is two.

JEE Main · 2023 · 31 Jan 2023 · Shift 2 · Integer answer