Which has the least entropy :

Options

A. Graphite
B. Diamond
C. `N_(2)(g)`
D. `N_(2)O(g)`

Explanation

To determine which substance has the least entropy among the given options, we need to analyze the molecular structure and the degree of randomness of each substance.

### Step-by-Step Solution:

1. **Understanding Entropy**:
- Entropy (S) is a measure of the degree of randomness or disorder in a system. The higher the entropy, the more disordered the system is.

2. **Analyzing the Options**:
- **Option A: Graphite**:
- Graphite has a layered structure where the layers are held together by weak van der Waals forces. This allows the layers to slide over each other, leading to a moderate degree of randomness.

- **Option B: Diamond**:
- Diamond has a tetrahedral arrangement of carbon atoms with strong covalent bonds. The atoms are rigidly fixed in place, resulting in very low molecular movement and thus very low entropy.

- **Option C: Nitrogen (N2)**:
- Nitrogen is a diatomic gas with relatively weak intermolecular forces. Gases generally have high entropy due to the freedom of movement of their molecules.

- **Option D: Nitrous Oxide (N2O)**:
- N2O is also a gas and, like nitrogen, has weak intermolecular forces, contributing to a high degree of randomness.

3. **Comparing Entropy**:
- Among the four options, diamond has the strongest intermolecular forces and the least molecular movement, which leads to the least randomness or entropy.
- Graphite, while having some degree of order, allows for more movement than diamond, thus having higher entropy.
- Both nitrogen and nitrous oxide, being gases, have significantly higher entropy due to the freedom of movement of their molecules.

4. **Conclusion**:
- Therefore, the substance with the least entropy is **Option B: Diamond**.

### Final Answer:
**Option B: Diamond has the least entropy.**