Which of the following statement$(s)$ is/are incorrect?

Select the correct order for the elements $B, C, N, O$:

Consider the following:
$(I)$ The order of first ionisation enthalpy of the first three elements of the $3^{rd}$ period is $Mg > Al > Na$
$(II)$ The element with an electronegativity of $3.5$ is chlorine
$(III)$ The order of sizes of ions $Mg^{2+}, Na^{+}, F^{-}$ and $O^{2-}$ is $Mg^{2+} < Na^{+} < F^{-} < O^{2-}$
$(IV)$ The $IUPAC$ name of the element with atomic number $106$ is Bohrium.
The correct statements are

In general,the property (magnitudes only) that shows an opposite trend in comparison to other properties across a period is

Which of the following statements is incorrect?

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