Question

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

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

Answer 1

The Correct Option is B

To determine which ion Be^{2+} is isoelectronic with, we first need to understand the concept of isoelectronic species. Isoelectronic species are atoms, molecules, or ions that have the same number of electrons.

Let's find the number of electrons for each entity:

1. For Be^{2+}: Beryllium's atomic number is 4, meaning a neutral Beryllium atom has 4 electrons. The ion Be^{2+} has lost 2 electrons (due to its 2+ charge), so it has 2 electrons remaining.
2. For H^+: Hydrogen's atomic number is 1, meaning a neutral Hydrogen atom has 1 electron. The ion H^+ has lost 1 electron, so it has 0 electrons.
3. For Li^+: Lithium's atomic number is 3, meaning a neutral Lithium atom has 3 electrons. The ion Li^+ has lost 1 electron, so it has 2 electrons.
4. For Na^+: Sodium's atomic number is 11, meaning a neutral Sodium atom has 11 electrons. The ion Na^+ has lost 1 electron, so it has 10 electrons.
5. For Mg^{2+}: Magnesium's atomic number is 12, meaning a neutral Magnesium atom has 12 electrons. The ion Mg^{2+} has lost 2 electrons, so it has 10 electrons.

Based on the calculations above, the Li^+ ion has 2 electrons, which is the same as Be^{2+}. Therefore, Be^{2+} is isoelectronic with Li^+.

Correct Answer: Li^+