Question:
Which element from following forms superoxide with oxygen?
Which element from following forms superoxide with oxygen?
Show Hint
Larger alkali metal cations (K, Rb, Cs) stabilise the large superoxide ion.
Updated On: Oct 1, 2026
- Sodium
- Potassium
- Lithium
- Magnesium
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
On burning in excess oxygen, alkali metals give different oxides depending on the size of the cation. Lithium gives the normal oxide, sodium gives mainly the peroxide, and K, Rb and Cs give superoxides (\(\text{MO}_2\)).
Step 2: Why Size Matters:
The superoxide ion \(\text{O}_2^-\) is large. A large, weakly polarising cation such as \(\text{K}^+\) stabilises it through high lattice energy.
Step 3: Check Each Option:
Sodium: forms \(\text{Na}_2\text{O}_2\) (peroxide) mainly.
Potassium: forms \(\text{KO}_2\) (superoxide).
Lithium: forms \(\text{Li}_2\text{O}\) (normal oxide).
Magnesium: forms \(\text{MgO}\) (normal oxide).
Step 4: Conclusion:
Potassium is the only element in the list that forms a superoxide.
Final Answer:
Potassium forms the superoxide \(\text{KO}_2\), option (B). \[ \boxed{\text{(B) Potassium}} \]
On burning in excess oxygen, alkali metals give different oxides depending on the size of the cation. Lithium gives the normal oxide, sodium gives mainly the peroxide, and K, Rb and Cs give superoxides (\(\text{MO}_2\)).
Step 2: Why Size Matters:
The superoxide ion \(\text{O}_2^-\) is large. A large, weakly polarising cation such as \(\text{K}^+\) stabilises it through high lattice energy.
Step 3: Check Each Option:
Sodium: forms \(\text{Na}_2\text{O}_2\) (peroxide) mainly.
Potassium: forms \(\text{KO}_2\) (superoxide).
Lithium: forms \(\text{Li}_2\text{O}\) (normal oxide).
Magnesium: forms \(\text{MgO}\) (normal oxide).
Step 4: Conclusion:
Potassium is the only element in the list that forms a superoxide.
Final Answer:
Potassium forms the superoxide \(\text{KO}_2\), option (B). \[ \boxed{\text{(B) Potassium}} \]
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