Question

Which pair is of isoelectronic species?

• A. $K ^{+}, Cl ^{-}, Na ^{+}$
• B. $K^{+}, C l^{-}, C a^{2+}$
• C. $Fe ^{-}, Al ^{3+}, K ^{+}$
• D. $Fe ^{2+}, Cu ^{2+}, V ^{3+}$

Answer 1

Answer: (B)

Isoelectronic species have same number of electrons.

$K ^{+}:$ Number of electrons $=19-1=18$

${ }_{17} Cl ^{-}:$ Number of electrons $=17+1=18$

${ }_{20} Ca ^{2+}:$ Number of electrons $=20-2=18$

hence, $K ^{+}, Cl ^{-}$ and $Ca ^{2+}$ are isoelectronic species.