In going from fluorine to iodine

Options

A. Electron affinity increases
B. size increases
C. reactivity increases
D. ionisation energy increases.

Explanation

To solve the question "In going from fluorine to iodine," we need to analyze the trends in the properties of halogens as we move down the group in the periodic table. The halogens are located in Group 17 of the periodic table, and the elements in this group include fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

### Step-by-Step Solution:

1. **Identify the Elements**:
- The elements in question are fluorine (F) and iodine (I). They are both halogens.

2. **Understand the Trend in Atomic Size**:
- As we move down a group in the periodic table, the atomic size increases. This is because each successive element has an additional electron shell.
- Fluorine is in the second period, while iodine is in the fifth period. Therefore, iodine has more electron shells than fluorine.

3. **Evaluate Electron Affinity**:
- Electron affinity generally decreases as you move down a group. This is because the added electron is further from the nucleus and experiences more shielding from the inner electrons, making it less energetically favorable to gain an electron.
- Thus, the electron affinity of iodine is less than that of fluorine.

4. **Assess Reactivity**:
- Reactivity of nonmetals like halogens generally decreases as you move down the group. Fluorine is the most reactive halogen, while iodine is less reactive.
- This trend is due to the increased atomic size and decreased electronegativity down the group.

5. **Consider Ionization Energy**:
- Ionization energy also decreases as you move down a group. It is easier to remove an electron from iodine than from fluorine because iodine's outer electrons are further from the nucleus and are less tightly held.
- Therefore, the ionization energy of iodine is lower than that of fluorine.

6. **Conclusion**:
- Among the options given (electro affinity, size, reactivity, ionization energy), the only correct statement is that the size increases when going from fluorine to iodine.

### Final Answer:
- The correct answer is: **Size will increase**.