Among lanthanoids, Ln (III) compounds are predominant. However, occasionally in solutions or in solid compounds, +2 and +4 ions are also obtained.

Explanation

To understand why Ln(III) compounds are predominant among lanthanides, while +2 and +4 oxidation states are occasionally observed, we can break down the explanation into several steps:

### Step 1: Understand the Common Oxidation State
Lanthanoids primarily exhibit a +3 oxidation state (Ln(III)) due to the loss of three electrons from their outermost shells. This is the most stable and common oxidation state for these elements.

### Step 2: Consider the Electronic Configuration
The lanthanides have the general electronic configuration of [Xe] 6s² 4f¹⁴ 5d¹⁰. When they lose three electrons to form Ln(III), they typically lose the two 6s electrons and one 4f electron.

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