The decreasing nucleophilic order of the following compounds is:
i. `NH_(3)`, ii. `PH_(3)`, iii. `AsH_(3)`, iv. `SbH_(3)`

Options

A. `(i) gt (ii) gt (iii) gt (iv)`
B. `(iv) gt (iii) gt (ii) gt (i)`
C. `(ii) gt (i) gt (iii) gt (iv)`
D. `(ii) gt (i) gt (iv) gt (iii)`

Explanation

To determine the decreasing nucleophilic order of the compounds NH₃, PH₃, AsH₃, and SbH₃, we need to analyze the nature of these compounds as nucleophiles, which are species that donate electron pairs. Here’s a step-by-step breakdown of the reasoning:

### Step 1: Identify the Compounds
The compounds given are:
1. NH₃ (Ammonia)
2. PH₃ (Phosphine)
3. AsH₃ (Arsine)
4. SbH₃ (Stibine)

### Step 2: Understand Nucleophilicity
Nucleophilicity is influenced by the ability of an atom to donate its lone pair of electrons. The central atom's size and electronegativity play crucial roles in determining this ability.

### Step 3: Analyze the Group Trend
These compounds belong to Group 15 of the periodic table. As we move down the group from nitrogen to antimony:
- The size of the central atom increases (N < P < As < Sb).
- The electronegativity decreases (N > P > As > Sb).

### Step 4: Basicity vs. Nucleophilicity
- Basicity refers to the ability to accept protons (H⁺), which is generally stronger for smaller atoms with higher electronegativity.
- Nucleophilicity, however, is the ability to donate electrons, which increases with larger atomic size in the same group, as the lone pair becomes more available for donation.

### Step 5: Determine the Nucleophilic Order
Based on the above analysis:
- NH₃ is the least nucleophilic because it is the smallest and most electronegative, making it a stronger base but a weaker nucleophile.
- PH₃ is slightly more nucleophilic than NH₃ due to its larger size.
- AsH₃ is more nucleophilic than PH₃.
- SbH₃ is the most nucleophilic due to its larger size and lower electronegativity, allowing for easier donation of the lone pair.

### Conclusion
Thus, the decreasing order of nucleophilicity is:
**SbH₃ > AsH₃ > PH₃ > NH₃**

### Final Answer
The correct order is **SbH₃ > AsH₃ > PH₃ > NH₃**.

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