Which of the following statements is/are incorrect?

Given below are two statements $:$
Statement $(I) :$ The radii of isoelectronic species increase in the order $Mg^{2+} < Na^{+} < F^{-} < O^{2-}$.
Statement $(II) :$ The magnitude of electron gain enthalpy of halogens decreases in the order $Cl > F > Br > I$.
In the light of the above statements,choose the most appropriate answer from the options given below $:$

Which one of the following sets of ions represents the collection of isoelectronic species?

Which of the following statements are correct?
$A.$ The process of the addition of an electron to a neutral gaseous atom is always exothermic.
$B.$ The process of removing an electron from an isolated gaseous atom is always endothermic.
$C.$ The $1^{st}$ ionization energy of boron is less than that of beryllium.
$D.$ The electronegativity of $C$ is $2.5$ in $CH_4$ and $CCl_4$.
$E.$ $Li$ is the most electropositive among elements of group $I$.
Choose the correct answer from the options given below:

Which of the following orders is incorrect?

Count the number of properties which have higher value for '$O$' atom than that of '$S$': Ionisation potential, Electron affinity, Covalent radius, Electronegativity.