As a group, all of the f-block elements (those that use their remaining electrons to fill an f sublevel orbital) are known as the
a. actinide series
c. lanthanide series
b. inner transition metals
d. transition metals

As a group, all of the f-block elements (those that use their remaining electrons to fill an f sublevel orbital) are known as the inner transition metals. They are called as such because they help transition from the s-block and d-block in the 6th and 7th periods. Their outermost electrons can be found in the f-orbital. The f-block elements are divided into two series: actinides (6th period) and lanthanides (7th period).