Question

$Be^{2+}$ is isoelectronic with which of the following ions?

• A. $H^+$
• B. $Li^+$
• C. $Na^+$
• D. $Mg^{2+}$

Answer 1

Answer: (B)

$Li^+$

Answer 2

Isoelectronic species contain same number of electrons. $Be^{2+}$ contains 2 electrons.
Among the given options, only $Li^+$ contains 2 electrons and therefore, it is isoelectronic with $Be^{2+}$.
$H^+ \rightarrow no eletron Na^+ \rightarrow 10e^-$
$Li^+ \rightarrow 2 e^-$
$Mg^{2+} \rightarrow 10 e^-$
Hence, $Be^{2+}$ is isoelectronic with $Li^+$.