Which has least covalent radius?

Which pair of elements has maximum electronegativity difference?

In which of the following arrangements, the order is not strictly according to the property written against it?

The ionic radii $$(\mathop A\limits^o)$$ of $$\mathrm{C}^{4-}$$ and $$\mathrm{O}^{2-}$$ respectively are 2.60 and 1.40. The ionic radius of the isoelectronic ion $$\mathrm{N}^{3-}$$ would be