To determine the correct order of atomic or ionic radii, we will analyze the trends in atomic size across the periodic table, focusing on the d-block elements as discussed in the video transcript.
### Step-by-Step Solution:
1. **Understanding Atomic Radius Trends**:
- Atomic radius generally decreases across a period from left to right due to the increase in effective nuclear charge (Z_eff) as protons are added to the nucleus without a significant increase in shielding from inner electrons.
2. **Analyzing the d-block Elements**:
- The d-block elements (transition metals) include elements such as Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), and Zinc (Zn).
- As we move from Sc to Zn, the number of d-electrons increases.
3. **Effect of d-electrons**:
- The d-electrons have a poor shielding effect. As the d-electrons increase, they contribute to an increase in effective nuclear charge, leading to a decrease in atomic size.
- However, after a certain point (especially from Co to Zn), the d-electrons start to exhibit a screening effect, which can counteract the increase in effective nuclear charge, leading to an increase in atomic size.
4. **Order of Atomic Radii**:
- For the first few d-block elements (Sc to Cr), the atomic radius decreases due to the increasing effective nuclear charge.
- For the later d-block elements (Co to Zn), the atomic radius may not decrease consistently due to the increased screening effect.
5. **Conclusion**:
- The correct order of atomic/ionic radii for the given elements is Sc < Ti < V < Cr < Mn < Fe < Co < Ni < Cu < Zn. This indicates that as we move from Scandium to Zinc, the atomic radius decreases initially and then may increase slightly due to the reasons discussed.
### Final Answer:
The correct order of atomic/ionic radii is: **Sc < Ti < V < Cr < Mn < Fe < Co < Ni < Cu < Zn**.
