Question

Which one of the following species is isoelectronic with P3-?
(A) Kr
(B) Ca2
(C) Na
(D) F​

Answer 1

Answer:

Isoelectronic means “having the same number of electrons”. For example: F– and Na+ are both isoelectronic with Ne. The isoelectronic series associated with Argon is: P3–, S2–, Cl–, Ar, K+, Ca2+, Ga3+ a.

Answer 2

(B) Ca2+ is the correct answer.

• Isoelectronic species refers to the species which have same number of electrons.
• Looking at the electronic configuration of all the given elements and ions, we will compare their number of electrons.

• Electronic configuration of P3- : 1s²2s²2p⁶3s²3p⁶
• Number of electrons in P3- : 18

• Electronic configuration of Kr : 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶
• Number of electrons in Kr : 36

• Electronic configuration of Ca²+ : 1s²2s²2p⁶3s²3p⁶
• Number of electrons in Ca²+ : 18

• Electronic configuration of Na : 1s²2s²2p⁶3s¹
• Number of electrons in Na : 11

• Electronic configuration of F : 1s²2s²2p⁵
• Number of electrons in F : 9

Here, both Ca2+ and P3- have same number of electrons i.e. 18 and hence they are isoelectronic species.