For which of the following is $Z_{eff}$ equal to $Z$?

Between $2s$ and $2p$ electrons,which one experiences a greater shielding effect from inner shells?

Which of the following statements is incorrect?

Which of the following statements is correct about the "shielding effect"?
$1$. It is effective when the orbitals in the inner shells are completely filled.
$2$. Inner shells do not show any effect.
$3$. With an increase of shielding down the group,ionization energy increases.
$4$. With increasing nuclear charge,the shielding effect increases.

Among the following,the energy of $2s$ orbital is lowest in

For the valence shell of $Na$,screening is provided by: