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).

alkaline metals are lithium, sodium, rubidium, potassium, cesium and francium.

alkali metals have electronegativity from 0.7 to 1, lowest in periodic table of elements, which means that alkali metals (i group in periodic table) has positive oxidation number in compounds.

electronegativity is a chemical property that describes the tendency of an atom to attract a shared pair of electrons towards itself.

alkaline metals (far left in main group) have lowest ionizations energy and easy remove valence electrons,

for example, potassium is the alkali metal and has a single valence electron in the outer electron shell.

electron configuration of potassium is: ₁₉k 1s²2s²2p⁶3s²3p⁶4s¹.

they can not exist alone in nature, because they are very reactive.