Which among the following elements has the highest first ionization enthalpy?

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A:$ The energy required to form $Mg^{2+}$ from $Mg$ is much higher than that required to produce $Mg^{+}$.
Reason $R:$ $Mg^{2+}$ is a small ion and carries more charge than $Mg^{+}$.
In the light of the above statements,choose the correct answer from the options given below:

Element having highest $I.P.$ value is

The first ionization enthalpy $(\Delta_{i} H)$ values of the third period elements,$Na, Mg$ and $Si$ are respectively $496, 737$ and $786 \, kJ \, mol^{-1}$. Predict whether the first $\Delta_{i} H$ value for $Al$ will be more close to $575$ or $760 \, kJ \, mol^{-1}$? Justify your answer.

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

The set representing the correct order of first ionisation potential is