Which of the following can show variable valency ?

Options

A. F
B. Cl
C. Br
D. I

Answer

To determine which of the given elements can show variable valency, we need to analyze the electronic configurations and the ability of these elements to utilize their d-orbitals for bonding.

### Step-by-Step Solution:

1. **Identify the Elements and Their Electronic Configurations:**
- **Fluorine (F):** Atomic number 9, electronic configuration: 1s² 2s² 2p⁵
- **Chlorine (Cl):** Atomic number 17, electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁵
- **Bromine (Br):** Atomic number 35, electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁵
- **Iodine (I):** Atomic number 53, electronic configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 4p⁶ 5s² 5p⁵

2. **Analyze the Valency of Each Element:**
- **Fluorine:** Has 7 valence electrons (2s² 2p⁵) and typically gains 1 electron to achieve a stable octet, showing a valency of -1 (monovalent). It does not have vacant d-orbitals to promote electrons, thus it does not show variable valency.
- **Chlorine:** Has 7 valence electrons (3s² 3p⁵) and can lose or gain electrons. Chlorine can show multiple oxidation states (+1, +3, +5, +7) due to the presence of vacant 3d orbitals, allowing for promotion of electrons.
- **Bromine:** Similar to chlorine, bromine has 7 valence electrons (4s² 4p⁵) and can also show multiple oxidation states (+1, +3, +5, +7) due to available 4d orbitals.
- **Iodine:** Also has 7 valence electrons (5s² 5p⁵) and can show multiple oxidation states (+1, +3, +5, +7) because of the presence of 5d orbitals.

3. **Conclusion:**
- The elements that can show variable valency are **Chlorine, Bromine, and Iodine**. Fluorine does not show variable valency.

### Final Answer:
Chlorine, Bromine, and Iodine can show variable valency.