Test Index

VITEEE 2009 Paper

Question : 58 of 120

Marks: +1, -0

Assertion (A) : K. Rb and Cs form superoxides.

Reason (R) : The stability of the superoxides increases from 'K' to 'Cs' due to decrease in lattice energy.

The correct answer is

Both (A) and (R) are true and (R) is the correct explanation of (A)
Both (A) and (R) are true but (R) is not the correct explanation of (A)
(A) is true but (R) is not true
(A) is not true but (R) is true

Validate

Solution:

The species having an O-O bond and 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\text{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 'K' to 'Cs' also increases.

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