In a given shell,the order of screening effect is

Arrange $s, p, d,$ and $f$ subshells of a shell in the increasing order of effective nuclear charge $(Z_{eff})$ experienced by the electron present in them.

If $Z_{eff}$ of boron is $x$,then $Z_{eff}$ of oxygen will be

The core charge on oxygen is equal to $-$

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

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.