On what ground can you say that scandium `(Z=21)` is a transition element but zinc `(Z=30)` is not?

Explanation

To determine why scandium (Z=21) is classified as a transition element while zinc (Z=30) is not, we need to analyze their electronic configurations and the definition of transition elements.

### Step 1: Write the electronic configurations
- **Scandium (Z=21)**: The electronic configuration is \( [Ar] 3d^1 4s^2 \).
- **Zinc (Z=30)**: The electronic configuration is \( [Ar] 3d^{10} 4s^2 \).

### Step 2: Understand the definition of transition elements
According to IUPAC, transition elements are defined as elements that have an incomplete d-subshell in one or more of their oxidation states. This means that for an element to be classified as a transition metal, it must have the ability to lose electrons from its d-orbitals.
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