Which of the following alkali metals form complex hydrides?

Options

A. Li
B. Na
C. K
D. Both A and B

Answer

To solve the question "Which of the following alkali metals form complex hydrides?" we will analyze the properties of the alkali metals provided: lithium (Li), sodium (Na), and potassium (K).

### Step-by-Step Solution:

1. **Understanding Complex Hydrides**:
- Complex hydrides are compounds that contain hydrogen and a metal, where the metal can form coordination complexes. Alkali metals can form such compounds with certain hydrides.

2. **Identifying Alkali Metals**:
- The alkali metals mentioned in the question are lithium (Li), sodium (Na), and potassium (K).

3. **Examining Lithium**:
- Lithium is known to form complex hydrides such as lithium aluminum hydride (LiAlH4). This compound is widely used as a reducing agent in organic chemistry.

4. **Examining Sodium**:
- Sodium also forms complex hydrides, notably sodium borohydride (NaBH4). This compound is used as a reducing agent and is important in various chemical reactions.

5. **Examining Potassium**:
- Potassium does not typically form complex hydrides like lithium and sodium do. It primarily forms simple hydrides (KH) rather than complex ones.

6. **Conclusion**:
- Based on the analysis, both lithium and sodium form complex hydrides, while potassium does not. Therefore, the correct answer is that both lithium and sodium form complex hydrides.

### Final Answer:
- The correct option is **both A and B (lithium and sodium)**.