In a group of elements,as the atomic number increases,which of the following is $NOT$ observed?

The electronic configurations of elements $A, B$ and $C$ are $[He] 2s^1$,$[Ne] 3s^1$ and $[Ar] 4s^1$ respectively. Which one of the following orders is correct for the first ionization potentials (in $kJ \ mol^{-1}$) of $A, B$ and $C$?

Electronic configurations of four elements $A$,$B$,$C$,$D$ are given below:
$A$) $1s^2 2s^2 2p^6 3s^1$
$B$) $1s^2 2s^2 2p^6 3s^2 3p^1$
$C$) $1s^2 2s^2 2p^6 3s^2$
$D$) $1s^2 2s^2 2p^6 3s^2 3p^2$
The correct order of first ionization enthalpy of these elements is:

Mercury is the only metal which is liquid at $0 \, ^oC$. This is due to its:

The correct order of first ionization enthalpy for the given four elements is:

The first ionization enthalpy of $Na$,$Mg$ and $Si$,respectively,are: $496, 737$ and $786 \ kJ \ mol^{-1}$. The first ionization enthalpy $(kJ \ mol^{-1})$ of $Al$ is