What is the difference between the ionization energy of inner-shell electrons and the ionization energy of outer-shell electrons?

Question

A. The ionization energy of inner-shell electrons changes with respect to the ionization energy of outer-shell electrons.
B. They are equal to each other.
C. The ionization energy of inner-shell electrons is greater than the ionization energy of outer-shell electrons.
D. The ionization energy of inner-shell electrons is less than the ionization energy of outer-shell electrons.

Answer 1

The answer is C

The inner-shell electrons are bound more tightly to the nucleus - the effective nuclear charge acting on them is higher (due to the lower distance and shielding effect) - than the outer shell electrons. Hence, more energy is needed to remove them.