Transition elements, also known as transition metals, are a group of elements that have partially filled d orbitals in their atom or ion. They are located in the d-block of the periodic table, between the s-block and p-block elements. Transition elements exhibit similar chemical properties, including the ability to form complex compounds, variable oxidation states, and the ability to act as catalysts.

In the given options, the element that is not considered as a part of transition elements is Zinc (Zn).

Explanation:

1. Definition of Transition Elements:
- Transition elements are a group of elements that have partially filled d orbitals in their atom or ion.
- They are located in the d-block of the periodic table.

2. Characteristics of Transition Elements:
- Transition elements exhibit similar chemical properties.
- They have variable oxidation states.
- They can form complex compounds.
- They can act as catalysts.

3. Analysis of the Options:
a) Zinc (Zn):
- Zinc is not considered a transition element because it has a completely filled d orbital (d10 configuration) in its atom or ion.
- It does not exhibit the characteristic of having partially filled d orbitals.
- Therefore, option A is the correct answer.

b) Copper (Cu):
- Copper is a transition element as it has partially filled d orbitals (d10s1 configuration) in its atom or ion.
- It exhibits the characteristic properties of transition elements.

c) Zirconium (Zr):
- Zirconium is a transition element as it has partially filled d orbitals (d2s2 configuration) in its atom or ion.
- It exhibits the characteristic properties of transition elements.

d) Silver (Ag):
- Silver is a transition element as it has partially filled d orbitals (d10s1 configuration) in its atom or ion.
- It exhibits the characteristic properties of transition elements.

Therefore, the element that is not considered a part of transition elements is Zinc (Zn) because it does not have partially filled d orbitals in its atom or ion.