Question

In which pair are the two species Isoelectronic?

• A. $\mathrm{Ne},{\mathrm{F}}^{-}$
• B. $\mathrm{Ar},{\mathrm{Be}}^{2+}$
• C. $\mathrm{K},{\mathrm{F}}^{-}$
• D. ${\mathrm{S}}^{2-},\mathrm{He}$

Answer 1

The correct option is A

$\mathrm{Ne},{\mathrm{F}}^{-}$

Explanation for the correct option:

Option(A):$\mathrm{Ne},{\mathrm{F}}^{-}$

• Species that have the same number of electrons or ions are known to be isoelectronic species.
• We can find isoelectronic species by adding the number of electrons in each atom of the species and the charge.
• Here Neon and Fluorine are isoelectronic species as the Fluorine ion has 10 electrons making it isoelectronic with Neon having the same 10 electrons.

Explanation for the incorrect option:

Option(B):$\mathrm{Ar},{\mathrm{Be}}^{2+}$

• Argon has 18 electrons whereas${\mathrm{Be}}^{+2}$ has only 2 electrons in it.
• Hence, the given Option is the incorrect one.

Option(C):$\mathrm{K},{\mathrm{F}}^{-}$

• Here the Potassium has 19 whereas ${\mathrm{F}}^{-}$ has only 10 electrons in it.
• Hence, the above-given Option does not represent the correct option.

Option(D):${\mathrm{S}}^{2-},\mathrm{He}$

• ${\mathrm{S}}^{-2}$ has 18 whereas Helium has only 2 electrons in it.
• Thus the given Option is an incorrect one.

Therefore, the pair having the two species Isoelectronic is given as option (A) $\mathrm{Ne},{\mathrm{F}}^{-}$.