In the reaction `3Mg + N_(2) rarr Mg_(3) N_(2)`, Nitrogen is oxidised or reduced.

Answer

To determine whether nitrogen is oxidized or reduced in the reaction \(3Mg + N_2 \rightarrow Mg_3N_2\), we need to analyze the oxidation states of nitrogen before and after the reaction.

### Step-by-Step Solution:

1. **Identify the Reactants and Products:**
- Reactants: \(3Mg\) and \(N_2\)
- Product: \(Mg_3N_2\)

2. **Determine the Oxidation State of Nitrogen in \(N_2\):**
- In elemental form (as in \(N_2\)), the oxidation state of nitrogen is 0.

3. **Determine the Oxidation State of Nitrogen in \(Mg_3N_2\):**
- The oxidation state of magnesium (Mg) is +2.
- In \(Mg_3N_2\), there are 3 magnesium atoms, contributing a total of \(3 \times (+2) = +6\).
- Let the oxidation state of nitrogen be \(x\). Since there are 2 nitrogen atoms, the total contribution from nitrogen is \(2x\).
- The overall charge of the compound \(Mg_3N_2\) is neutral (0), so we can set up the equation:
\[ 3(+2) + 2x = 0 \]
\[ 6 + 2x = 0 \]
\[ 2x = -6 \]
\[ x = -3 \]
- Therefore, the oxidation state of nitrogen in \(Mg_3N_2\) is -3.

4. **Compare the Oxidation States:**
- In the reactants, the oxidation state of nitrogen is 0 (in \(N_2\)).
- In the products, the oxidation state of nitrogen is -3 (in \(Mg_3N_2\)).

5. **Determine if Nitrogen is Oxidized or Reduced:**
- A decrease in oxidation state (from 0 to -3) indicates that nitrogen has gained electrons.
- Gaining electrons corresponds to reduction.

### Conclusion:
- Therefore, nitrogen is **reduced** in the reaction \(3Mg + N_2 \rightarrow Mg_3N_2\).