Zinc, cadmium and mercury are generally not considered as transition metals. Give reasons.

Explanation

### Step-by-Step Solution:

1. **Understanding Transition Metals**:
Transition metals are defined as elements that have an incomplete d-subshell in one or more of their oxidation states. This characteristic allows them to exhibit variable oxidation states and form colored compounds.

**Hint**: Remember that the key feature of transition metals is their ability to have partially filled d-orbitals.

2. **Electronic Configuration of Zinc, Cadmium, and Mercury**:
...