What is effective nuclear charge and shielding effect?

Q. What does penetration of electrons mean?does it has anything to do with nuclear charge or shielding effect? Explain with diagram.

Q. 14. What is inert pair effct , screening effect or shielding effect or Z-effect

Q. Explain effective nuclear charge & shielding effect & Factor on which shielding effect depends.

Q. In this formula-nuclear charge =atomic number-shielding effect There shuold be penetration effect instead of shielding effect Isn't it

Q. What is meant by effective nuclear charge?