Of the following isoelectronic ions,the one which has the lowest ionisation potential is

Which of the following represents the correct decreasing order of the first ionization energy for $Ba$,$Sr$,$Ca$,and $Mg$?

Given below are two statements:
Statement $I$: The decrease in first ionization enthalpy from $B$ to $Al$ is much larger than that from $Al$ to $Ga$.
Statement $II$: The $d$ orbitals in $Ga$ are completely filled.
In the light of the above statements,choose the most appropriate answer from the options given below:

The first ionisation energy of lithium $(Li)$ will be

The correct order of ionisation energy of $C$,$N$,$O$,and $F$ is

The first ionization energy is the lowest for which of the following elements?