Which statement is correct regarding ionisation potential?

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:

Which of the following elements has the lowest ionisation potential?

In the given graph,which point represents an alkali metal with the least atomic number?

The graph shows the variation of Ionization Potential $(I.P.)$ with Atomic Number $(At. No.)$ for elements $A$ to $E$. If these elements belong to the same group in the periodic table,identify the group.

Explain the trend observed in ionisation enthalpy when moving from top to bottom in the same group of the periodic table.