The $CORRECT$ order of first ionisation enthalpy is:

The correct order of second ionisation potentials $(IP)$ of $Ca$,$Ba$ and $K$ is

What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?

Find the formula of the halide of a metal whose successive ionization energies are $10, 16, 25, 400, 500 \ eV \ mol^{-1}$ respectively $:-$

Given below are two statements: One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: The first ionization enthalpy of $O$ is lower than that of $N$ and $F$.
Reason $R$: The loss of an electron from $O$ leads to a stable half-filled $p$ orbital.
In light of the above statements, choose the most appropriate answer from the options given below:

The first ionization energy of alkaline earth metals is higher than that of alkali metals. This is due to...