Choose the elements which from monovalent ions :
(i) Li (ii) Ca (iii) F (iv) Al (v) P (vi) K

Answer

To determine which elements form monovalent ions from the given list, we need to analyze the valency of each element. Monovalent ions are those that can lose or gain one electron to achieve a stable electronic configuration.

### Step-by-Step Solution:

1. **Identify the Elements**: The elements provided are:
- (i) Li (Lithium)
- (ii) Ca (Calcium)
- (iii) F (Fluorine)
- (iv) Al (Aluminum)
- (v) P (Phosphorus)
- (vi) K (Potassium)

2. **Analyze Each Element**:
- **(i) Lithium (Li)**:
- Atomic number: 3
- Electronic configuration: 1s² 2s¹
- Lithium has one electron in its outermost shell and can lose this electron to form Li⁺.
- **Conclusion**: Monovalent ion.

- **(ii) Calcium (Ca)**:
- Atomic number: 20
- Electronic configuration: 1s² 2s² 2p⁶ 3s²
- Calcium has two electrons in its outermost shell and can lose both to form Ca²⁺.
- **Conclusion**: Not a monovalent ion.

- **(iii) Fluorine (F)**:
- Atomic number: 9
- Electronic configuration: 1s² 2s² 2p⁵
- Fluorine has seven electrons in its outermost shell and can gain one electron to form F⁻.
- **Conclusion**: Monovalent ion.

- **(iv) Aluminum (Al)**:
- Atomic number: 13
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p¹
- Aluminum has three electrons in its outermost shell and typically loses three electrons to form Al³⁺.
- **Conclusion**: Not a monovalent ion.

- **(v) Phosphorus (P)**:
- Atomic number: 15
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p³
- Phosphorus has five electrons in its outermost shell and can gain or share three electrons to form P³⁻ or P⁺³.
- **Conclusion**: Not a monovalent ion.

- **(vi) Potassium (K)**:
- Atomic number: 19
- Electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹
- Potassium has one electron in its outermost shell and can lose this electron to form K⁺.
- **Conclusion**: Monovalent ion.

3. **Final Selection**: The elements that form monovalent ions are:
- Lithium (Li)
- Fluorine (F)
- Potassium (K)

### Final Answer:
The elements which form monovalent ions are: **Li, F, K**.