Question

How many of the following radius orders are incorrect?
(a) $N^{3 -}>P^{3 -}$
(b) $O^{2 -}>F^{-}$
(c) $Ca^{2 +}>Sr^{2 +}$
(d) $S^{-}>S^{2 -}$
(e) $S^{2 -}>O^{-}$

Answer 1

Since, ionic radii decreases in a period and increases in a group
$P^{3 -}>N^{3 -}$
$O^{- 2}>F^{-}$
$Sr^{+ 2}>Ca^{+ 2}$
$S^{- 2}>S^{-}$
$S^{- 2}>O^{-}$
For isoelectronic species, greater will be the Atomic number lesser will be radii.If ions are derived from different atoms, is known as isoelectronic species. All the ions have the same number of electrons in their electronic shells and have same electronic configuration but their nuclear charge will be different nuclear charge due to number of protons in the nucleus with increase in the number protons in the nucleus the electrons will be more attracted towards nucleus causing the decrease in ionic radius.
Hence, (b) and (e) are correct.