Question

Which among the following pairs are not having the same number of total electrons?

• A. \( \text{Na}^+ \) and \( \text{Al}^{3+} \)
• B. \( \text{O}^{2-} \) and \( \text{F}^- \)
• C. \( \text{Mg}^{2+} \) and Ar
• D. \( \text{P}^{3-} \) and Ar

Hint:

When comparing ions and neutral atoms, count the electrons based on the atomic number and charge of the ion or atom to determine whether they have the same number of electrons.

Answer 1

The Correct Option is A

The total number of electrons in an ion is determined by its atomic number and charge: - \( \text{Na}^+ \) has 10 electrons (Na: atomic number 11, loses 1 electron). - \( \text{Al}^{3+} \) has 10 electrons (Al: atomic number 13, loses 3 electrons). Therefore, \( \text{Na}^+ \) and \( \text{Al}^{3+} \) have the same number of electrons, making this pair correct. Let's analyze other pairs: - \( \text{O}^{2-} \) has 10 electrons (O: atomic number 8, gains 2 electrons), and \( \text{F}^- \) has 10 electrons (F: atomic number 9, gains 1 electron). This pair also has the same number of electrons. - \( \text{Mg}^{2+} \) has 10 electrons (Mg: atomic number 12, loses 2 electrons), while Ar has 18 electrons. This pair does not have the same number of electrons. - \( \text{P}^{3-} \) has 18 electrons (P: atomic number 15, gains 3 electrons), and Ar has 18 electrons. This pair has the same number of electrons. The correct answer is \( \text{Mg}^{2+} \) and Ar.