Which of the following atomic species has maximum ionisation energy?

Which factors influence the value of ionization enthalpy?

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

$B$ has a smaller first ionization enthalpy than $Be$. Consider the following statements:
$(I)$ It is easier to remove a $2p$ electron than a $2s$ electron.
$(II)$ The $2p$ electron of $B$ is more shielded from the nucleus by the inner core of electrons than the $2s$ electrons of $Be$.
$(III)$ The $2s$ electron has more penetration power than the $2p$ electron.
$(IV)$ The atomic radius of $B$ is more than $Be$.
(Atomic number: $B=5, Be=4$)
The correct statements are:

Generally,the first ionisation energy increases along a period. But there are some exceptions. The one which is not an exception is

Which electrons are removed to determine the ionization enthalpy of beryllium and boron,respectively?