How does the shielding effect caused by inner electrons affect the ionisation energy?

Explanation

(i) The electrons of inner shells form a cloud of negative charge. This cloud shields the oute electron from the nucleus and also acts as a screen between the nucleus and the electrons.
(ii) This screen reduces the coulombic attraction between the positive nucleus and the negan outer electrons. Therefore, the outer electrons do not feel the full effect of the positive of the nucleus.
If screening effect increases, ionization energy decreases.