Among the following options,the sequence of increasing first ionisation potential will be

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$:
Assertion $A:$ The first ionisation enthalpy decreases across a period.
Reason $R:$ The increasing nuclear charge outweighs the shielding across the period.
In the light of the above statements,choose the most appropriate from the options given below:

The first ionization enthalpy values (in $kJ\,mol^{-1}$) of group $13$ elements are :

$B$	$801$
$Al$	$577$
$Ga$	$579$
$In$	$558$
$Tl$	$589$

How would you explain this deviation from the general trend?

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

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?

Which of the following has the least ionization potential?