Question

ASSERTION: K, Rb and Cs form superoxides.
REASON: The stability of the superoxides increases from 'K' to 'Cs' due to decrease in lattice energy.
A.Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
B.Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
C.Assertion is correct but Reason is incorrect
D.Both Assertion and Reason are incorrect

Answer 1

${K^ + },{\text{ }}R{b^ + }$ and $C{s^ + }$ are large cations and superoxide ion is bigger than oxide and peroxide ions. Because of the higher lattice energies, a large cation stabilizes a large anion, hence these metals form Superoxides.

Complete step wise answer:
There is a direct relationship between the stability of a superoxide and the low electronegativity of the accompanying cation. Only alkali metals obviously form stable superoxide, and alkali-earth ones can be found as impurities in the peroxides also superoxide ion is large, so the stability of the compound is superiority by the size of the cation is the smallest one that forms the superoxide with comparative ease, while $Na{O_2}$ is hard to obtain and $Li{O_2}$ has never been isolated (both Cs and Rb form stable superoxide). K, Rb, Cs from superoxides when they are exposed to fire in the air. As long as we move down the group, the size of an atom from k to Cs increases, so lattice energy decreases and therefore the stability of superoxide also decreases. Potassium, rubidium and cesium react with dioxygen to form the superoxide.
Correct reason: Since for salts of larger anions, the lattice energy increases with increase in the size of the cation from ${K^ + }$ to $C{s^ + }$ , therefore, the stability of their superoxides will increases from K to Cs.

Therefore, the correct answer is option (C).

Note: As we go down in the periodic table, Group 1 that is alkali metals hold their single outer valence electron more loosely, and so reactivity increases. Below potassium (Na, Li), we can store the metal in oil with no difficulty. Above potassium (Rb, Cs), the need to eliminate all oxygen to prevent reaction in air. Potassium (K) is the absolutely unique element where one can obviously store it in oil, but it is highly seen to react with any available oxygen to form explosive peroxides. The atomic size of Li is very small, so it can form only oxide. As we go down the first most group, the atomic size of the atom increases and so the holding capacity also. Therefore, lithium forms oxide, sodium forms peroxide while potassium forms superoxide.