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

Options

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

Explanation

To solve the question regarding the substance that gives a brick red flame and breaks down on heating to give oxygen and a brown gas, we can follow these steps:

### Step 1: Identify the Flame Color
The question states that the substance gives a brick red flame. In the context of s-block elements, certain metal salts produce characteristic flame colors.

- **Brick Red Flame**: This is typically associated with lithium salts. However, in the context of nitrates, we need to consider other options as well.

### Step 2: Analyze the Given Options
The options provided are:
- A) Magnesium nitrate
- B) Calcium nitrate
- C) Barium nitrate
- D) Strontium nitrate

We need to evaluate these nitrates based on their thermal decomposition products.

### Step 3: Thermal Decomposition of Nitrates
When nitrates decompose upon heating, they generally produce a metal oxide, nitrogen dioxide (NO2), and oxygen (O2). We need to check which of these nitrates fits the criteria of producing a brown gas (NO2) and oxygen.

1. **Magnesium Nitrate (Mg(NO3)2)**: Decomposes to MgO, NO2, and O2 but does not produce a brick red flame.
2. **Calcium Nitrate (Ca(NO3)2)**: Decomposes to CaO, NO2, and O2. It does not produce a brick red flame.
3. **Barium Nitrate (Ba(NO3)2)**: Decomposes to BaO, NO2, and O2. Barium compounds produce a green flame, not brick red.
4. **Strontium Nitrate (Sr(NO3)2)**: Decomposes to SrO, NO2, and O2. Strontium compounds produce a crimson or red flame.

### Step 4: Conclusion
Among the options, Strontium nitrate (D) fits the criteria of producing a brick red flame and decomposing to give oxygen and a brown gas (NO2).

Thus, the correct answer is:
**D) Strontium nitrate**