In the following given elements choose which of them is/are transition element and why ?
`Zn, Cd, Ag, Fe, Ni`

Explanation

To determine which of the given elements are transition elements, we need to understand the definition of transition elements and analyze the electron configurations of the elements provided: Zn, Cd, Ag, Fe, and Ni.

### Step-by-Step Solution:

1. **Definition of Transition Elements**:
Transition elements are defined as elements that have an incomplete d-subshell in any of their oxidation states. This means that at least one of the d-orbitals must not be fully filled with electrons.

2. **Electron Configurations**:
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