Which is least basic ? `SbH_(3)PH_3,NH_3,AsH_3`

Explanation

To determine which of the given hydrides (SbH₃, PH₃, NH₃, and AsH₃) is the least basic, we can analyze the basicity of each compound based on the properties of their central atoms and their electronic configurations.

### Step-by-Step Solution:

1. **Identify the Central Atoms and Their Electronic Configurations**:
- **NH₃ (Ammonia)**: The central atom is Nitrogen (N), with the electronic configuration of 1s² 2s² 2p³. It has a lone pair of electrons available for bonding, making it a good base.
- **PH₃ (Phosphine)**: The central atom is Phosphorus (P), with the electronic configuration of 1s² 2s² 2p⁶ 3s² 3p³. It also has a lone pair but is less basic than NH₃ due to larger atomic size and lower electronegativity.
- **AsH₃ (Arsenic Hydride)**: The central atom is Arsenic (As), with the electronic configuration of 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p³. As we move down the group, the size increases, and the basicity decreases.
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