The core charge on oxygen is equal to $-$

The bromine atom possesses $35$ electrons. It contains $6$ electrons in $2p$ orbital,$6$ electrons in $3p$ orbital and $5$ electrons in $4p$ orbital. Which of these electrons experiences the lowest effective nuclear charge?

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.

Explain the relationship between the energy of orbitals in the same subshell and the atomic number,with an example.

Among the following pairs of orbitals,which orbital will experience the larger effective nuclear charge?
$(i)$ $2s$ and $3s$
$(ii)$ $4d$ and $4f$
$(iii)$ $3d$ and $3p$

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