Which of the following is electron deficient ?

Options

A. `(SiH_(3))_(2)`
B. `(BH_(3))_(2)`
C. `PH_(3)`
D. `(CH_(3))_(2)`

Explanation

To determine which of the given species is electron deficient, we need to analyze the valence electrons and bonding of each species. Let's go through each option step by step.

### Step 1: Analyze SiH3 (Silicon Trihydride)
1. **Valence Electrons**: Silicon (Si) has 4 valence electrons, and each hydrogen (H) has 1 valence electron.
2. **Bonding**: In SiH3, silicon forms three single bonds with three hydrogen atoms.
3. **Electron Count**:
- Silicon contributes 4 electrons (from 3 bonds with H).
- Each hydrogen contributes 1 electron (3 H atoms contribute 3 electrons).
- Total = 4 (from Si) + 3 (from H) = 7 electrons.
4. **Octet Check**: Silicon has 4 electrons in bonding and does not complete its octet (needs 8). Thus, SiH3 is electron deficient.

### Step 2: Analyze B2H6 (Diborane)
1. **Valence Electrons**: Boron (B) has 3 valence electrons, and there are 2 boron atoms and 6 hydrogen atoms.
2. **Bonding**: In B2H6, each boron atom forms three bonds, including 3-center 2-electron bonds (banana bonds).
3. **Electron Count**:
- Each boron contributes 3 electrons, totaling 6 from both boron atoms.
- Each hydrogen contributes 1 electron (6 H atoms contribute 6 electrons).
- Total = 6 (from B) + 6 (from H) = 12 electrons.
4. **Octet Check**: Each boron has only 6 electrons around it (3 bonds), hence they do not complete their octet. Thus, B2H6 is also electron deficient.

### Step 3: Analyze PH3 (Phosphine)
1. **Valence Electrons**: Phosphorus (P) has 5 valence electrons, and each hydrogen has 1 valence electron.
2. **Bonding**: In PH3, phosphorus forms three single bonds with three hydrogen atoms.
3. **Electron Count**:
- Phosphorus contributes 5 electrons (3 bonds with H).
- Each hydrogen contributes 1 electron (3 H atoms contribute 3 electrons).
- Total = 5 (from P) + 3 (from H) = 8 electrons.
4. **Octet Check**: Phosphorus has 8 electrons around it (3 bonds), hence it is not electron deficient.

### Step 4: Analyze C2H6 (Ethane)
1. **Valence Electrons**: Carbon (C) has 4 valence electrons, and there are 2 carbon atoms and 6 hydrogen atoms.
2. **Bonding**: In C2H6, each carbon forms four single bonds (3 with H and 1 with another C).
3. **Electron Count**:
- Each carbon contributes 4 electrons (2 C atoms contribute 8 electrons).
- Each hydrogen contributes 1 electron (6 H atoms contribute 6 electrons).
- Total = 8 (from C) + 6 (from H) = 14 electrons.
4. **Octet Check**: Each carbon has 8 electrons around it (4 bonds), hence it is not electron deficient.

### Conclusion
From the analysis, we find that SiH3 and B2H6 are electron deficient species. However, the question asks for which of the following is electron deficient. Therefore, the answer is **B2H6**.