Assertion :- Equivalent weight of `NH_(3)` in the reaction `N_(2) rarrNH_(3)` is `17//3` while that of `N_(2)` is `28//6`.
Reason :- `"Equivalent weight" =("Molecular weight")/("number of "e^(-)" lost or gained/mole")`

Explanation

To solve the question, we need to analyze the assertion and reason regarding the equivalent weights of NH₃ and N₂ in the reaction N₂ → NH₃.

### Step-by-Step Solution:

1. **Identify the Reaction**:
The reaction we are considering is:
\[ N_2 \rightarrow NH_3 \]

2. **Determine the Oxidation States**:
- In \(N_2\), nitrogen has an oxidation state of 0.
- In \(NH_3\), nitrogen has an oxidation state of -3.

3. **Calculate the Change in Electrons**:
- The change in oxidation state from 0 to -3 indicates that nitrogen is gaining electrons.
- Each nitrogen atom in \(N_2\) gains 3 electrons. Since there are 2 nitrogen atoms in \(N_2\), the total number of electrons gained is:
\[ 2 \times 3 = 6 \text{ electrons} \]

4. **Calculate the Equivalent Weight of NH₃**:
- The molecular weight (gram molecular mass, GMM) of \(NH_3\) is 17 g/mol.
- The number of electrons gained per mole (N factor) for \(NH_3\) is 3.
- Therefore, the equivalent weight of \(NH_3\) is calculated as:
\[ \text{Equivalent weight of } NH_3 = \frac{\text{Molecular weight}}{\text{N factor}} = \frac{17}{3} \text{ g/equiv} \]

5. **Calculate the Equivalent Weight of N₂**:
- The molecular weight of \(N_2\) is 28 g/mol.
- The N factor for \(N_2\) is the total number of electrons gained by both nitrogen atoms, which is 6 (as calculated earlier).
- Thus, the equivalent weight of \(N_2\) is:
\[ \text{Equivalent weight of } N_2 = \frac{\text{Molecular weight}}{\text{N factor}} = \frac{28}{6} \text{ g/equiv} \]

6. **Conclusion**:
- The assertion states that the equivalent weight of \(NH_3\) is \(17/3\) and that of \(N_2\) is \(28/6\). Both of these calculations are correct.
- The reason provided states that "Equivalent weight = (Molecular weight) / (number of electrons lost or gained per mole)", which is indeed the formula used to derive the equivalent weights.

### Final Answer:
- Both the assertion and reason are correct, and the reason is the correct explanation of the assertion.