Which of the following can evolve more than one gas (vapour) if heated in dry test tube.

Options

A. `naNO_(3)(s)`
B. `MgCO_(3)(s)`
C. `FeSO_(4)(s)`
D. `(NH_(4))_(2)Cr_(2)O_(7)(s)`

Answer

To determine which compound can evolve more than one gas when heated in a dry test tube, we will analyze each of the given compounds step by step:

### Step 1: Analyze Sodium Nitrate (NaNO3)
- **Heating Reaction**: When sodium nitrate is heated, it decomposes to form sodium nitrite (NaNO2) and oxygen gas (O2).
- **Gas Evolved**: Only one gas (O2) is evolved.

**Hint**: Check the decomposition products to see how many gases are produced.

### Step 2: Analyze Magnesium Carbonate (MgCO3)
- **Heating Reaction**: When magnesium carbonate is heated, it decomposes to form magnesium oxide (MgO) and carbon dioxide gas (CO2).
- **Gas Evolved**: Only one gas (CO2) is evolved.

**Hint**: Look for the gaseous products in the decomposition reaction.

### Step 3: Analyze Iron Sulfide (FeS)
- **Heating Reaction**: When iron sulfide is heated, it decomposes to form ferric oxide (Fe2O3) along with the evolution of sulfur dioxide (SO2) and sulfur trioxide (SO3) gases.
- **Gas Evolved**: Two gases (SO2 and SO3) are evolved.

**Hint**: Identify if multiple gaseous products are formed during the reaction.

### Step 4: Analyze Ammonium Dichromate (NH4O2Cr2O7)
- **Heating Reaction**: When ammonium dichromate is heated, it decomposes to form chromium oxide (Cr2O3), water (H2O), and nitrogen gas (N2).
- **Gas Evolved**: Only one gas (N2) is evolved.

**Hint**: Consider both gaseous and non-gaseous products when analyzing the reaction.

### Conclusion:
Among the compounds analyzed, only **Iron Sulfide (FeS)** evolves more than one gas (sulfur dioxide and sulfur trioxide) when heated in a dry test tube. Therefore, the correct answer is **FeS**.

**Final Answer**: Iron Sulfide (FeS) evolves more than one gas when heated.