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Question: Answered & Verified by Expert
Assertion (A) K, Rb and Cs form superoxides.
Reason (R) The stability of the superoxides increases from ' $\mathrm{K}$ ' to ' $\mathrm{Cs}$ ' due to decrease in lattice energy.
The correct answer is
Chemistrys Block ElementsTS EAMCETTS EAMCET 2009
Options:
  • A Both (A) and (R) are true and (R) is the correct explanation of (A)
  • B Both (A) and (R) are true but (R) is not the
    correct explanation of (A)
  • C (A) is true but (R) is not true
  • D (A) is not true but (R) is true
Solution:
1901 Upvotes Verified Answer
The correct answer is: (A) is true but (R) is not true
Superoxides are the species having an $\mathrm{O}-\mathrm{O}$ bond and $\mathrm{O}$ in an oxidation state of $-\frac{1}{2}$ (superoxide ion is $\mathrm{O}_2^{-}$). Usually these are formed by active metals such as $\mathrm{KO}_2, \mathrm{RbO}_2$ and $\mathrm{CsO}_2$. For the salts 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 of the superoxides from ' $\mathrm{K}$ ' to 'Cs' also increases.

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