In any transition series, from left to right, the d-orbitals are progressively filled and their properties vary accordingly.
Q. Which element do you expect to have the smallest atomic radius?

Options

A. La
B. Zn
C. Sc
D. Hg

Explanation

To determine which element has the smallest atomic radius among the given elements (Scandium, Lanthanum, Zinc, and Mercury), we can follow these steps:

### Step 1: Identify the Elements and Their Positions
- Scandium (Sc) has an atomic number of 21.
- Zinc (Zn) has an atomic number of 30.
- Lanthanum (La) has an atomic number of 57.
- Mercury (Hg) has an atomic number of 80.

### Step 2: Understand the Trends in Atomic Radius
- As we move **from left to right** across a period, the atomic radius **decreases** due to the increase in nuclear charge, which pulls the electrons closer to the nucleus.
- As we move **down a group**, the atomic radius **increases** because of the addition of electron shells, which outweighs the effect of increasing nuclear charge.

### Step 3: Analyze the Periods of the Elements
- Scandium (Sc) and Zinc (Zn) are in the **4th period**.
- Lanthanum (La) and Mercury (Hg) are in the **6th period**.

### Step 4: Compare Atomic Radii of Elements
- Between Scandium and Lanthanum, Lanthanum will have a **larger atomic radius** because it is in a lower period.
- Between Zinc and Mercury, Mercury will have a **larger atomic radius** because it is also in a lower period.

### Step 5: Compare the Remaining Elements
- Now we compare the atomic radii:
- Lanthanum (La) > Scandium (Sc)
- Mercury (Hg) > Zinc (Zn)

### Conclusion
- The order of atomic radii from largest to smallest is: Lanthanum > Mercury > Scandium > Zinc.
- Therefore, **Zinc (Zn)** has the smallest atomic radius among the given elements.

### Final Answer
The element with the smallest atomic radius is **Zinc (Zn)**.

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