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
K and Rb form stable superoxides, but Cs has an ionization enthalpy less than 400 kJ/mol.
Thus, the correct answer is 2, as K and Rb are the metals that meet the criteria.
Let one focus of the hyperbola $ \frac{x^2}{a^2} - \frac{y^2}{b^2} = 1 $ be at $ (\sqrt{10}, 0) $, and the corresponding directrix be $ x = \frac{\sqrt{10}}{2} $. If $ e $ and $ l $ are the eccentricity and the latus rectum respectively, then $ 9(e^2 + l) $ is equal to:
The largest $ n \in \mathbb{N} $ such that $ 3^n $ divides 50! is: