Question

How would you distinguish between the first, second, and third ionization energies of an atom?

Answer 1

Ionization energy is the energy used by some foreign species to remove electrons from any other species. So, ionization energy is directly related to the removal of electrons from any species.

Complete answer:
As by the definition of ionization energy which is given in the hint part it is clear that it is the amount of energy which is required for the removal of electrons. So, the basic difference between the first, second, and third ionization energies of an atom are as follow:
-As the name ‘first ionization energy’ suggested, it is that amount of energy which is required for the removal of 1st electron from the outermost shell when an atom is present in the neutral state.
-As the name ‘second ionization energy’ suggested, it is that amount of energy which is required for the removal of 2nd electron from the shell when an atom is present in $+ 1$ oxidation state.
-As the name ‘third ionization energy’ suggested, it is that amount of energy which is required for the removal of 3rd electron from the shell when an atom is present in $+ 2$ oxidation state.
-And the numerical value of ionization energy increases from first to second, second to third, third to fourth, and so on.

Note:
Here some of you may think that second and third ionization energy is that energy which is required for the removal of two and three electrons respectively from the atom, which is wrong. So, don’t get confused with the words like two (2) and second (2nd).