The most common oxidation state exhibited by lanthanoids and actinoids is ..................

Explanation

To determine the most common oxidation state exhibited by lanthanoids and actinoids, we can follow these steps:

### Step 1: Understand the Lanthanoids
- **Lanthanoids** are elements with atomic numbers from 57 (Lanthanum) to 71 (Lutetium).
- The general electronic configuration for lanthanoids is \( [Xe] 4f^{0-14} 5d^{0-1} 6s^{2} \).

### Step 2: Identify Possible Oxidation States of Lanthanoids
- The common oxidation states for lanthanoids include +2, +3, and +4.
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