Which of the following elements has the lowest ionization energy?

The successive ionisation enthalpies of an element $X$ in $(kJ \ mol^{-1})$ are $1012$,$1907$,$2955$,$4955$,$6275$ and $21,260$ respectively. The element $X$ is:

Which diagram of ionization energy is correct for the elements $Cu$,$Ag$,and $Au$?

The first ionisation energy of oxygen is less than that of nitrogen. Which of the following is the correct reason for this observation?

The correct order of $C$,$N$,$O$ and $F$ in terms of second ionisation potential is

How would you explain the fact that the first ionization enthalpy of sodium is lower than that of magnesium but its second ionization enthalpy is higher than that of magnesium?