A thermal decomposition method that yields very pure nitrogen uses the following as reactant(s):

Options

A. Barium azide
B. Sodium nitride
C. Ammonium chloride
D. Magnesium nitride

Answer

To determine which thermal decomposition method yields very pure nitrogen, we will analyze the decomposition reactions of various compounds mentioned in the question.

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactants mentioned are barium azide (Ba(N3)2), sodium azide (NaN3), sodium nitride (Na3N), aluminum chloride (AlCl3), and magnesium nitride (Mg3N2).

2. **Thermal Decomposition of Barium Azide**:
- The reaction is:
\[ \text{Ba(N}_3\text{)}_2 \xrightarrow{\text{heat}} \text{Ba} + 3 \text{N}_2 \]
- This reaction produces barium and three moles of nitrogen gas (N2).

3. **Thermal Decomposition of Sodium Azide**:
- The reaction is:
\[ 2 \text{NaN}_3 \xrightarrow{\text{heat}} 2 \text{Na} + 3 \text{N}_2 \]
- This reaction also produces sodium and three moles of nitrogen gas (N2).

4. **Thermal Decomposition of Sodium Nitride**:
- The reaction is:
\[ 2 \text{Na}_3\text{N} \xrightarrow{\text{heat}} 6 \text{Na} + \text{N}_2 \]
- This reaction produces sodium and one mole of nitrogen gas (N2), but it is not as efficient in producing nitrogen compared to the previous two.

5. **Thermal Decomposition of Aluminum Chloride**:
- The reaction is:
\[ 2 \text{AlCl}_3 \xrightarrow{\text{heat}} 2 \text{Al} + 3 \text{Cl}_2 \]
- This reaction does not produce nitrogen at all.

6. **Thermal Decomposition of Magnesium Nitride**:
- The reaction is:
\[ \text{Mg}_3\text{N}_2 \xrightarrow{\text{heat}} 3 \text{Mg} + \text{N}_2 \]
- This reaction yields nitrogen gas, but it is not as pure as the nitrogen obtained from barium azide or sodium azide.

7. **Conclusion**: The thermal decomposition of barium azide and sodium azide yields very pure nitrogen gas. Among these, barium azide is often highlighted for producing very pure nitrogen.

### Final Answer:
The thermal decomposition method that yields very pure nitrogen uses **barium azide (Ba(N3)2)** as the reactant.

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