Which of the following statements is incorrect?

Which one among the following statements is/are not correct?
$I$. $Ba$ compounds,generally are more covalent than $Be$ compounds.
$II$. The electron gain enthalpy of $He$ is positive.
$III$. The oxidation state of $O$ in $OF_2$ and $Na_2O$ are same.
$IV$. The radius of $Na^{+}$ ion is smaller than that of $F^{-}$ ion.

Which of the following statements is not correct?

The element with a very high ionization enthalpy but zero electron gain enthalpy is ....

Point out the wrong statement: On moving horizontally from left to right across a period in the periodic table

Outermost electronic configuration of a group $13$ element,$E$,is $4s^2 4p^1$. The electronic configuration of an element of $p$-block,period $5$,placed diagonally to element $E$ is: