A substance which gives a brick red flame and breaks down on heating giving oxygen and brown gas is:

Options

A. Calcium carbonate
B. Magnesium carbonate
C. Magnesium nitrate
D. Calcium nitrate

Explanation

To solve the question, we need to identify a substance that meets the following criteria:

1. It produces a brick red flame when burned.
2. It decomposes upon heating to release oxygen and a brown gas.

Let's break this down step by step:

### Step 1: Identify the Flame Color
The question states that the substance gives a brick red flame. In chemistry, certain metal compounds are known to produce characteristic flame colors.

- **Hint**: Research which metal ions produce a brick red flame.

### Step 2: Identify the Substance
The metal that imparts a brick red flame is calcium (Ca). Therefore, we should consider compounds containing calcium.

- **Hint**: Look for common calcium compounds that can decompose upon heating.

### Step 3: Consider Decomposition Products
We need to find a calcium compound that, when heated, decomposes to produce oxygen (O2) and a brown gas.

- **Hint**: Think about the decomposition reactions of calcium compounds, especially nitrates.

### Step 4: Analyze Calcium Nitrate
Calcium nitrate, which has the chemical formula Ca(NO3)2, is a suitable candidate. When heated, it decomposes as follows:

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

- Calcium oxide (CaO) is a solid.
- Nitrogen dioxide (NO2) is a brown gas.
- Oxygen (O2) is released as a gas.

- **Hint**: Verify the products of the decomposition reaction to ensure they match the criteria.

### Step 5: Conclusion
Based on the analysis, the substance that gives a brick red flame and decomposes to release oxygen and a brown gas is calcium nitrate (Ca(NO3)2).

- **Final Answer**: The correct answer is calcium nitrate.