Which series of elements have nearly the same atomic radii ?

Options

A. Fe , Co , Ni
B. Na , K , Rb
C. Li, Be, Mg
D. F, Cl , Br

Answer

To determine which series of elements have nearly the same atomic radii, we need to analyze the options provided and consider the trends in atomic radii across periods and groups in the periodic table.

### Step-by-Step Solution:

1. **Understanding Atomic Radii Trends**:
- Atomic radii generally decrease across a period from left to right due to increasing effective nuclear charge, which pulls the electrons closer to the nucleus.
- Atomic radii increase down a group due to the addition of electron shells, which outweighs the increase in nuclear charge.

2. **Analyzing the Options**:
- We are given four options to analyze. We will evaluate each one to see if the elements listed have similar atomic radii.

3. **Option 1**: Elements in Group 17 (Halogens)
- Example: Fluorine (F), Chlorine (Cl), Bromine (Br)
- As we move down the group, the atomic radius increases. Therefore, these elements do not have nearly the same atomic radii.

4. **Option 2**: Alkali Metals
- Example: Sodium (Na), Potassium (K), Rubidium (Rb)
- Similar to the first option, as we move down the group, the atomic radius increases significantly. Thus, these elements do not have nearly the same atomic radii.

5. **Option 3**: Elements in Period 2 and Period 3
- Example: Lithium (Li), Beryllium (Be), Magnesium (Mg)
- Here, we see that while there is a trend of increasing size down the group, the elements are from different periods, leading to different atomic sizes. So, they do not have nearly the same atomic radii.

6. **Option 4**: Transition Metals
- Example: Iron (Fe), Cobalt (Co), Nickel (Ni)
- These elements are all in the same period (4th period) and are transition metals. Due to poor shielding effects and electronic repulsions, the atomic radii of these elements tend to be very similar.

7. **Conclusion**:
- The series of elements that have nearly the same atomic radii is **Option 4: Iron (Fe), Cobalt (Co), Nickel (Ni)**.

### Final Answer:
The correct answer is **Option 4: Iron (Fe), Cobalt (Co), Nickel (Ni)**.