Lanthanoids that show +2 or +4 instead of +3

This type of question, asked 3 times: 2021 Paper 25, 26 Jun 2022, 28 Jun 2022. All 3 questions below, oldest first.

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Question 1
2021 Paper 25
47 $MO_{2}$
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Question 2
26 Jun 2022
129 $The most common oxidation state of Lanthanoid elements is +3. Which of the following is likely to deviate easily from +3 oxidation state?$
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Question 3
28 Jun 2022
38 $Which one of the lanthanoids given below is the most stable in divalent form?$
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