Q18 / 120 · VITEEE 2009 · Chemistry
Assertion (A) : $\mathrm{K}$. Rb and Cs form superoxides.
Reason $(\mathbf{R}):$ The stability of the superoxides increases from ' $\mathrm{K}$ ' to ' $\mathrm{Cs}$ ' due to decrease in lattice energy.
The correct answer is
- ABoth (A) and (R) are true and (R) is the correct explanation of (A)
- BBoth (A) and (R) are true but (R) is not the correct explanation of $(A)$
- Correct answerC(A) is true but (R) is not true
- D(A) is not true but (R) is true
Solution
The species having an $\mathrm{O}-\mathrm{O}$ bond and $\mathrm{O}$ in an oxidation state of $-\frac{1}{2}$ are super oxides and is represented as $\mathrm{O}_{2}^{-}$. Usually these are formed by active metals such as $\mathrm{KO}_{2}$, $\mathrm{RbO}_{2}$ and $\mathrm{CsO}_{2} .$ For the sal ts of larger anions (like $\mathrm{O}_{2}^{-}$), lattice energy increases in a group. Since, lattice energy is the driving force for the formation of an ionic compound and its stability, the stability o the superoxides from 'K' to 'Cs' als increases.
Hence, the correct answer is option: 'C'.