The element with the smallest size in the group is

Options

A. lithium
B. fluorine
C. sodium
D. oxygen

Explanation

To determine the element with the smallest size in the group, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Elements**: The elements mentioned in the question are lithium (Li), sodium (Na), oxygen (O), and fluorine (F).

2. **Locate the Elements in the Periodic Table**:
- Lithium (Li) is in Group 1 and Period 2.
- Sodium (Na) is in Group 1 and Period 3.
- Oxygen (O) is in Group 16 and Period 2.
- Fluorine (F) is in Group 17 and Period 2.

3. **Compare Sizes in the Same Period**:
- In Period 2, we have lithium (Li), oxygen (O), and fluorine (F).
- As we move from left to right across a period, atomic size decreases due to the increase in nuclear charge, which pulls the electrons closer to the nucleus.
- Therefore, among Li, O, and F, fluorine (F) will have the smallest size.

4. **Compare Sizes in the Same Group**:
- In Group 1, we compare lithium (Li) and sodium (Na).
- As we move down a group, atomic size increases because additional electron shells are added.
- Thus, sodium (Na) is larger than lithium (Li).

5. **Conclusion**:
- Since we are looking for the element with the smallest size overall, we find that fluorine (F) is the smallest among the elements discussed (Li, Na, O, F).

### Final Answer:
The element with the smallest size in the group is **Fluorine (F)**.

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