JEE Main & Advanced AIEEE Solved Paper-2004

Which one of the following sets of ions represents the collection of isoelectronic species? (At.\[nos.\,F=9,Cl=17,Na=11,Mg=12,\] \[Al=13,K=19,Ca=20,Sc=21)\]

A) \[{{K}^{+}},C{{a}^{2+}},S{{c}^{3+}},C{{l}^{-}}\]

B) \[N{{a}^{+}},C{{a}^{2+}},S{{c}^{3+}},{{F}^{-}}\]

C) \[{{K}^{+}},C{{l}^{-}},M{{g}^{2+}},S{{c}^{3+}}\]

D) \[N{{a}^{+}},M{{g}^{2+}},A{{l}^{3+}},C{{l}^{-}}\]

Correct Answer: A

Solution :

Species	Z	Electron gained or lost in the formation	Electrons
\[{{K}^{+}}\]	19	-1	18
\[C{{a}^{2+}}\]	20	-2	18
\[S{{c}^{3+}}\]	21	-3	18
\[C{{l}^{-}}\]	17	+1	18

In this set, all have 18 electrons. Thus, isoelectronic.