Three occurs much more frequently metal-metal bonding in the compounds of heavy transition elements (3d series ). Assign reason.

Explanation

**Step-by-Step Solution:**

1. **Understanding Transition Elements**: Transition elements, particularly in the 3d series, have a unique electronic configuration characterized by the presence of d electrons. The general electronic configuration for these elements is given by \( \text{[Noble Gas]} \, ns \, (n-1)d \).

2. **Electronic Configuration of 3d Series**: In the 3d series, the electronic configurations of the elements can be summarized as follows:
- Scandium (Sc): \( [Ar] \, 3d^1 \, 4s^2 \)
- Titanium (Ti): \( [Ar] \, 3d^2 \, 4s^2 \)
- Vanadium (V): \( [Ar] \, 3d^3 \, 4s^2 \)
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