Why some elements are called transition and inner transition elements?...​

They are so called because they come immediately after actinium (Ac) in the periodic table.

Explanation:

Fourteen elements from Th(90) to Lw(103) comprise actinide series, and are also called second inner transition series. Though actinium (Z=89) does not possess any 5f electrons, it is customary to study actinium with actinoids

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.

the answer is a) cell division.

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