Question

Which of the following is not isoelectronic?

• A.
• B.
• C.
• D.

Answer 1

The correct option is A

Let's calculate number of electrons for each molecule.

$C{H}_3^{+}\Rightarrow \begin{array}{c}C=6electrons\\ H_3=3electrons\end{array}\}-\text{1 electron[Because of + charge] = 8 electrons}$
$H_3{O}^{+}\Rightarrow \begin{array}{c}{H}_3\to 3electrons\\ O\to 8electrons\end{array}\}\text{- 1 electrons [Because of + charge] = 10 electrons}$
$N{H}_3\Rightarrow \begin{array}{c}N\to 7electrons\\ H_3\to 3electrons\end{array}\}\text{10 electrons}$

$C{H}_3^{-}\Rightarrow \begin{array}{c}C\to 6electrons\\ H_3\to 3electrons\end{array}\}+\text{1 electrons[Because of - charge] = 10 electrons}$
$\text{Therefore},H_3{O}^{+},N{H}_{3}and{C{H}_3}^{-}areiso-electronic$