Final answer:
Electrons should be removed from the highest 'n' shell and the highest energy subshell first. For ionization, ns orbital electrons are easier to remove before (n - 1)d or (n - 2)f electrons.
Step-by-step explanation:
The statement 'always remove electrons from the _______ shell (n) and subshell ____ first' refers to the process of ionization in which electrons are removed from an atom. When it comes to removing electrons, one should remove electrons from the highest 'n' shell first, and within that shell, the highest energy subshell (which usually follows the order of s, p, d, f) according to the Aufbau principle and principles of quantum mechanics.
For example, in the case of an atom with a completely filled 3d subshell and a partially filled 4s subshell, electrons are removed from the 4s subshell before the 3d subshell, since 4s is the highest energy level. Additionally, within a subshell, the s orbital electrons are easier to remove than the d or f electrons, hence, the high-energy ns electrons are lost first, followed by (n - 1)d or (n - 2)f electrons depending on the specific electron configuration of the atom.