Which of the following statements are correct ?

Options

A.
B. `RS^(Ө)` is less basic but a stronger nucleophile than `RO^(Ө)`.
C. `NH_3` is both a stronger base and a stronger nucleophilic than `H_2 O`
D. `RO^(Ө)` and `overset (Ө) O H` are both stronger bases and stronger nucleophile than `ROH` and `H_2 O`.

Explanation

To determine which statements are correct, we will analyze each statement based on the principles of acidity, basicity, and nucleophilicity.

### Step-by-Step Solution:

1. **Analyzing Statement A: Fugacity Order**
- The statement mentions that the order of fugacity is related to acidity. It states that "weaker the base, stronger the leaving group."
- This is correct because, in general, a weaker base is a better leaving group in nucleophilic substitution reactions. Thus, if the fugacity order follows the acidity order, this statement is true.

2. **Analyzing Statement B: RS- vs. RO-**
- The statement claims that RS- is the least basic but a stronger nucleophile than RO-.
- To analyze this, we note that RSH (thiol) is more acidic than ROH (alcohol), meaning RS- is less basic than RO-. However, RS- can be a stronger nucleophile than RO- due to the larger size of sulfur, which can stabilize the negative charge better than oxygen. Therefore, this statement is true.

3. **Analyzing Statement C: NH3 vs. H2O**
- The statement claims that NH3 is both a stronger base and a stronger nucleophile than H2O.
- Basicity is determined by the availability of the lone pair of electrons. NH3 has a lone pair that is less tightly held compared to H2O due to the higher electronegativity of oxygen. Thus, NH3 is indeed a stronger base than H2O.
- Nucleophilicity is also related to basicity, and since NH3 is a stronger base, it is also a stronger nucleophile than H2O. Therefore, this statement is true.

4. **Analyzing Statement D: RO- and OH- vs. ROH and H2O**
- The statement asserts that RO- and OH- are both stronger bases and stronger nucleophiles than ROH and H2O.
- This is true because RO- (alkoxide) and OH- (hydroxide) are both negatively charged and therefore stronger bases than their neutral counterparts (ROH and H2O). Additionally, stronger bases are generally stronger nucleophiles, making this statement true as well.

### Conclusion:
All statements A, B, C, and D are correct.