The atomic radius of elements of which of the following series would be nearly the same

Options

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

Explanation

To determine which series of elements has nearly the same atomic radius, we can analyze the options provided in the question step by step.

### Step 1: Analyze Option A (Sodium, Potassium, Rubidium)
- Sodium (Na), Potassium (K), and Rubidium (Rb) are all alkali metals and belong to the same group (Group 1) in the periodic table.
- As we move down a group, the atomic radius increases due to the addition of electron shells.
- Therefore, the atomic radii will not be nearly the same: Rb > K > Na.
- **Conclusion**: This option is incorrect.

### Step 2: Analyze Option B (Lithium, Beryllium, Boron)
- Lithium (Li), Beryllium (Be), and Boron (B) are in the same period (Period 2).
- As we move from left to right across a period, the atomic radius decreases due to increasing nuclear charge (more protons) which pulls the electrons closer to the nucleus.
- Thus, the atomic radii will be different: Li > Be > B.
- **Conclusion**: This option is also incorrect.

### Step 3: Analyze Option C (Fluorine, Chlorine, Bromine)
- Fluorine (F), Chlorine (Cl), and Bromine (Br) are halogens and belong to the same group (Group 17).
- Similar to the alkali metals, as we move down the group, the atomic radius increases: Br > Cl > F.
- Therefore, the atomic radii will not be nearly the same.
- **Conclusion**: This option is incorrect as well.

### Step 4: Analyze Option D (Iron, Cobalt, Nickel)
- Iron (Fe), Cobalt (Co), and Nickel (Ni) are transition metals and belong to the d-block of the periodic table.
- In the d-block, the atomic radius does not change significantly across the transition metals due to the balance between increasing nuclear charge and inter-electronic repulsion.
- The atomic radii of Fe, Co, and Ni are nearly the same because the effects of increasing nuclear charge are offset by the electron-electron repulsion in the d-orbitals.
- **Conclusion**: This option is correct as the atomic radii are nearly the same.

### Final Answer
The atomic radius of elements in option D (Iron, Cobalt, Nickel) would be nearly the same.

---