What electron subshell is being filled for the rare earth series of elements on the periodic table? what electron subshell is being filled for the actinide series?

Explanation:

The electron subshell being filled is defined by the differential electron, which is the last electron placed in the electron configuration.

The rare earth series involves 17 elements: scandium, yttrium and 15  lanthanides. The subshell filled for these elements are:

The actinide series includes 15 elements. The electron subshell filled for these elements is 5f (they are part of the f-block).