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You can assume the electron will be taken from the outermost shell (the valence shell) because these are the electrons with the highest energy and therefore will take the least amount of energy to remove. These outer electrons have the smallest effective nuclear charge and therefore are less strongly bound to the nucleus by electrostatic attraction. The first ionization energy will always be much lower than the second ionization energy because once one electron is removed, electron electron repulsion decreases and the shells will contract to the nucleus enough to have them more strongly bound (and thus will require more energy to remove an electron after one has already been removed).
First ionization energy is the energy needed to remove the outermost electron from an atom so it should be the outermost orbital! Second ionization energy is always greater than the first because the electron is more tightly held.
The outermost electrons will be the electrons that are most affected by another atom of high electronegativity. Since the inner electrons are shielding the outermost electrons for the full nuclear attraction of the nucleus, they are the easiest to remove.
Since the ionization energy is the energy that is required to remove an electron, this would be one of the electrons in the outermost shell. These electrons are also known as the valence electrons and are most likely to be able to be removed.
For the first ionization energy, the electron is taken from the outermost orbital. The electrons in the outermost orbital are so far removed from the nucleus and its dense positive charge (Zeff) that they require the least amount of energy to remove. This is why the first ionization energy is the smallest numerical value, as well.
The electron will be taken from the furthest orbital. This is the reason why second ionization energy is always higher than the first. When you take the first electron off, the pull of the protons become a little stronger, so the second ionization energy of the atom would be higher
Just a quick thing I wanted to add. I found that when I try to rush the problems that ask "which orbital will an electron be taken from" I accidentally take it from the d-orbital because it's usually what's "added last." So quick tip for these is to write out the electron configuration first for the neutral atom THEN looking at whichever orbital is last (highest energy/outermost shell) and taking it from there.
It will be taken from the valence electrons in the outer orbital because these are less tightly held to the nucleus since the other electrons in the inner shells are shielding them from the positive attraction of the protons in the nucleus.
I also want to add that the order of removing electrons is not always the reversal of the order of adding electrons (especially in metals). For example, cobalt's electron configuration is [Ar]3d^74s^2, where the 4s^2 orbital fills before the 3^d. However, when we remove 2 electrons to make Co^2+, we actually remove the 4s^2 orbitals instead of the 3d^7.
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