Which of the following oxides is formed when potassium metal is burnt in excess air ?

Options

A. `K_2O`
B. `K_2O_2`
C. `KO_2`
D. `KO`

Answer

To solve the question of which oxide is formed when potassium metal is burnt in excess air, we can follow these steps:

### Step 1: Understand the reaction of potassium with oxygen
When potassium (K) is exposed to air, it reacts with oxygen (O2). Potassium can react with oxygen in different ways depending on the amount of oxygen available.

### Step 2: Identify the products formed
In excess air, potassium primarily forms potassium superoxide (KO2). This is different from potassium oxide (K2O) or potassium peroxide (K2O2), which can form under limited oxygen conditions.

### Step 3: Write the chemical equation
The reaction can be represented by the following equation:
\[ 4K + O2 \rightarrow 2KO2 \]
This shows that four moles of potassium react with one mole of oxygen to produce two moles of potassium superoxide.

### Step 4: Select the correct option
Based on the above information, we conclude that the oxide formed when potassium is burnt in excess air is potassium superoxide (KO2).

### Final Answer
The correct answer is option C: KO2 (potassium superoxide).

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