Which of the following is an electron deficient molecule?

Options

A. `LiH`
B. `B_(2)H_(6)`
C. `LiBH_(4)`
D. `B_(3)N_(3)H_(6)`

Answer

To determine which of the given molecules is an electron deficient molecule, we need to understand the concept of electron deficiency. An electron deficient molecule is one that has fewer electrons than required for maximum stability, typically fewer than 8 electrons for main group elements.

### Step-by-Step Solution:

1. **Understanding Electron Deficiency**:
- Electron deficiency occurs when a molecule has fewer electrons than needed for a stable octet configuration. For most main group elements, this means having fewer than 8 electrons around the central atom.

2. **Analyzing the Options**:
- We will analyze each option provided to see if they are electron deficient.

3. **Option A: LiH (Lithium Hydride)**:
- Lithium (Li) has 1 valence electron and can form one bond with hydrogen (H), which has 1 valence electron.
- In LiH, lithium shares its one electron with hydrogen, resulting in a stable configuration for both.
- Total electrons involved = 2 (1 from Li and 1 from H).
- Conclusion: LiH is not electron deficient.

4. **Option B: B2H6 (Diborane)**:
- Diborane consists of 2 boron (B) atoms and 6 hydrogen (H) atoms.
- Each boron atom can form 3 bonds, but in B2H6, it forms 4 bonds (2 B-H and 2 B-B) using 12 electrons (6 from H and 6 from B).
- However, to satisfy the octet rule, it would require 16 electrons (8 for each boron atom).
- Conclusion: B2H6 is electron deficient because it has only 12 electrons available instead of the required 16.

5. **Option C: LiBH4 (Lithium Borohydride)**:
- Lithium borohydride consists of one lithium atom, one boron atom, and four hydrogen atoms.
- Boron can form 4 bonds (1 with Li and 4 with H), utilizing 8 electrons (4 from H and 1 from Li).
- Conclusion: LiBH4 is not electron deficient as it can achieve a stable configuration.

6. **Option D: B3N3H6 (Borazine)**:
- Borazine has a structure similar to benzene, consisting of alternating boron and nitrogen atoms with hydrogen atoms.
- Each boron can form 3 bonds, and nitrogen can form 3 bonds as well, leading to a stable configuration.
- Conclusion: B3N3H6 is not electron deficient.

7. **Final Conclusion**:
- After analyzing all options, the only electron deficient molecule is **B2H6**.

### Final Answer:
The electron deficient molecule is **B2H6**.