All the following decompes easily on heating to give oxygen except :

Options

A. barium peroxide
B. potassium dichromate
C. sodium nitrate
D. None of these

Explanation

To solve the question "All the following decompose easily on heating to give oxygen except:", we need to analyze the decomposition reactions of the given compounds. Let's go through each option step by step.

### Step 1: Analyze Barium Peroxide (BaO2)
- **Decomposition Reaction**: When barium peroxide is heated, it decomposes according to the following reaction:
\[ 2 \text{BaO}_2 \rightarrow 2 \text{BaO} + \text{O}_2 \]
- **Conclusion**: Barium peroxide decomposes easily on heating to give oxygen.

### Step 2: Analyze Potassium Dichromate (K2Cr2O7)
- **Decomposition Reaction**: When potassium dichromate is heated, it decomposes as follows:
\[ 2 \text{K}_2\text{Cr}_2\text{O}_7 \rightarrow 2 \text{K}_2\text{CrO}_4 + \text{Cr}_2\text{O}_3 + \text{O}_2 \]
- **Conclusion**: Potassium dichromate also decomposes easily on heating to give oxygen.

### Step 3: Analyze Sodium Nitrate (NaNO3)
- **Decomposition Reaction**: Sodium nitrate decomposes upon heating:
\[ 2 \text{NaNO}_3 \rightarrow 2 \text{NaNO}_2 + \text{O}_2 \]
- **Conclusion**: Sodium nitrate decomposes easily on heating to give oxygen.

### Step 4: Identify the Exception
- Since we have analyzed the three options (Barium Peroxide, Potassium Dichromate, and Sodium Nitrate) and found that all of them decompose to give oxygen, we need to check if there is an option that does not fit this pattern. The question states "except," which implies that one of the options does not produce oxygen upon heating.

### Final Conclusion
- If the fourth option is "none of these," it implies that all the previous options do produce oxygen. Therefore, the correct answer to the question is that all given options decompose to give oxygen, and there is no exception among them.

### Summary of the Answer
All the compounds listed (Barium Peroxide, Potassium Dichromate, and Sodium Nitrate) decompose easily on heating to give oxygen. Therefore, the answer is **none of these**.