Question

Which of the following species are isoelectronic? A. $S^{2-}$
B. $C^{4-}$
C. $Mg^{2+}$
D. $O^{-}$
E. $Al^{3+}$ Choose the correct answer from the options given below:

• A. A, B, C only
• B. B, C, D only
• C. B, C, E only
• D. C, D, E only

Hint:

Isoelectronic species contain equal number of electrons.

Answer 1

The Correct Option is C

Concept:
Isoelectronic species are species having the same number of electrons.
Step 1:
Sulphur has atomic number 16. \[ S^{2-}=16+2=18~electrons \]
Step 2:
\[ C^{4-}=6+4=10 \] \[ Mg^{2+}=12-2=10 \] \[ O^{-}=8+1=9 \] \[ Al^{3+}=13-3=10 \]
Step 3:
Species having same electrons are: \[ C^{4-},\quad Mg^{2+},\quad Al^{3+} \] All contain: \[ 10~electrons \]
Step 4:
Hence correct answer is: \[ \boxed{\text{B, C, E}} \] \[ \boxed{\text{Correct Option = (3)}} \]