The core charge on oxygen is equal to $-$

In which pair does the first element have a higher $Z_{eff}$ than the second atom?

Effective nuclear charge is maximum in case of

The unpaired electrons in $Al$ and $Si$ are present in the $3p$ orbital. Which electrons will experience a higher effective nuclear charge from the nucleus?

The screening effect of $d$-electrons is

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.