Which of halogen has the greatest tendency to form monovalent anion X ?

Options

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

Answer

To determine which halogen has the greatest tendency to form a monovalent anion (X^-), we need to analyze the halogens: fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

### Step-by-Step Solution:

1. **Understanding Monovalent Anions**:
- A monovalent anion is formed when an atom gains one electron. For halogens, this means that F, Cl, Br, and I can each gain one electron to form F^-, Cl^-, Br^-, and I^- respectively.

2. **Electron Affinity**:
- The tendency to form anions is closely related to the electron affinity of the elements. Electron affinity is the energy change that occurs when an electron is added to a neutral atom. Higher electron affinity means a greater tendency to gain an electron.

3. **Trends in Halogens**:
- As we move down the group from fluorine to iodine, the size of the atoms increases. This increase in size affects the stability of the negative charge when the atom gains an electron.

4. **Stability of the Negative Charge**:
- A larger atomic radius means that the added electron is further from the nucleus, which can lead to a more stable anion due to decreased charge density (charge per unit area).
- Therefore, the stability of the negative charge increases down the group.

5. **Comparing the Halogens**:
- Fluorine (F) has the highest electronegativity and a very high electron affinity, but due to its small size, the added electron experiences a strong repulsion from the nucleus.
- Chlorine (Cl) has a lower electronegativity than fluorine but a larger atomic size, which allows for better stabilization of the negative charge.
- Bromine (Br) and iodine (I) continue this trend, with iodine being the largest and thus having the most stable anion.

6. **Conclusion**:
- Among the halogens, iodine (I) has the greatest tendency to form a monovalent anion (I^-) because it can stabilize the negative charge the best due to its larger atomic size.

### Final Answer:
Iodine (I) has the greatest tendency to form a monovalent anion (I^-).