A substance which gives brick red flame and breaks down on heating to give oxygen and a brown gas, is

Options

A. magnesium nitrate
B. calcium nitrate
C. barium nitrate
D. strontium nitrate

Explanation

To solve the question, we need to identify the substance that gives a brick red flame and decomposes upon heating to produce oxygen and a brown gas. Let's break it down step by step:

### Step 1: Understanding the Requirements
- The substance must produce a **brick red flame**.
- Upon heating, it must break down to give **oxygen (O2)** and a **brown gas**.

### Step 2: Identifying the Brown Gas
From the information provided, we know that the only common brown gas produced from nitrates is **nitrogen dioxide (NO2)**. This will help us narrow down our options.

### Step 3: Analyzing the Options
We have four options, all of which are nitrates. We need to check which of these can produce a brick red flame and also decompose to give O2 and NO2.

1. **Magnesium Nitrate (Mg(NO3)2)**:
- Magnesium does not produce any color in the flame test because it forms a protective oxide layer (MgO).
- **Conclusion**: Not the correct answer.

2. **Calcium Nitrate (Ca(NO3)2)**:
- Calcium produces a **brick red flame** when burned.
- On heating, calcium nitrate decomposes to form calcium oxide (CaO), oxygen (O2), and nitrogen dioxide (NO2).
- **Conclusion**: This could be the correct answer.

3. **Barium Nitrate (Ba(NO3)2)**:
- Barium produces a **pale green flame**.
- **Conclusion**: Not the correct answer.

4. **Strontium Nitrate (Sr(NO3)2)**:
- Strontium produces a **red flame**, but it is not specified as brick red.
- **Conclusion**: This is not the correct answer as it does not meet the specific requirement.

### Step 4: Confirming the Reaction of Calcium Nitrate
To further confirm that calcium nitrate is the correct answer, we can write the decomposition reaction:

\[ \text{2 Ca(NO}_3\text{)}_2 \rightarrow \text{2 CaO} + \text{O}_2 + \text{4 NO}_2 \]

This reaction shows that upon heating, calcium nitrate decomposes to produce calcium oxide, oxygen, and nitrogen dioxide, which is the brown gas we identified.

### Conclusion
Based on the analysis, the substance that gives a brick red flame and breaks down on heating to give oxygen and a brown gas is **Calcium Nitrate (Ca(NO3)2)**.

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