What is the common oxidation state shown by lanthanoids?

Solution

1. Lanthanoids belong to the 4f series of the f-block elements.
2. The general electronic configuration of lanthanoids is $[\text{Xe}]4f^{1-14}5d^{0-1}6s^2$.
3. They readily lose three electrons to achieve a stable configuration.
4. Hence the answer is (B).