Question

Which from the following elements form superoxide with air?

• A. Li
• B. Na
• C. K
• D. Mg

Hint:

Larger alkali metals such as potassium and rubidium tend to form superoxides, while lithium forms oxides and sodium forms peroxides.

Answer 1

The Correct Option is C

Step 1: Understand superoxide formation.
A superoxide is a compound in which the oxygen molecule exists as \( O_2^{2-} \). Alkali metals such as potassium (K), sodium (Na), and lithium (Li) can form superoxides when they react with oxygen, but the formation is selective based on the size of the metal ions.

Step 2: Lithium (Li) reaction with oxygen.
Lithium forms lithium oxide (Li2O), not a superoxide, with oxygen. This is because lithium has a small ionic radius and the formation of \( Li_2O \) is more favorable than forming a superoxide.

Step 3: Sodium (Na) reaction with oxygen.
Sodium forms sodium peroxide (Na2O2) when reacted with oxygen, not a superoxide.

Step 4: Potassium (K) reaction with oxygen.
Potassium, due to its larger ionic size compared to lithium and sodium, forms potassium superoxide (\( KO_2 \)) when reacted with oxygen.

Step 5: Magnesium (Mg) reaction with oxygen.
Magnesium does not form superoxide; it forms magnesium oxide (\( MgO \)) when reacted with oxygen.

Step 6: Final answer.
Thus, the element that forms a superoxide with air is Potassium (K), and the correct answer is option (3).