Why in any transition series, melting points first increase and then decrease and also they show a dip in the middle?

Explanation

### Step-by-Step Solution:

1. **Understanding the Transition Series:**
- Transition metals are elements found in the d-block of the periodic table. They have partially filled d-orbitals, which play a crucial role in determining their physical properties, including melting points.

2. **Initial Increase in Melting Points:**
- As we move across a transition series, the number of unpaired electrons in the d-orbitals increases.
- More unpaired electrons lead to stronger metallic bonding because unpaired electrons can participate in bonding interactions, enhancing the overall strength of the metallic bond.
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