The correct order of first ionisation enthalpy of the given elements is:

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:

Would you expect the first ionization enthalpies for two isotopes of the same element to be the same or different? Justify your answer.

For the second period elements,the correct increasing order of first ionisation enthalpy is:

Which of the following represents the correct decreasing order of the first ionization energy for $Ba$,$Sr$,$Ca$,and $Mg$?

Which electronic configuration shows the minimum first ionisation energy?