Question

In which pair does each species have the same number of unpaired electrons? A Al and Cu2+ B Ca and Cr3+ C Ca and Ni2+ D Fe3+ and O2–

Answer 1

The pair of species that have the same number of unpaired electrons is (option D) Fe³⁺ and O²⁻, as Fe³⁺ has 5 unpaired electrons in its d orbitals and O²⁻ also has 2 unpaired electrons in its p orbitals.

Step-by-step explanation:

The question is asking us to identify the pair of species that have the same number of unpaired electrons. We have to examine the electronic configuration of the given pairs of elements and ions. Looking at the options:

1. Al has 3 unpaired electrons in its 3p orbitals.
2. Cu²⁺ has 1 unpaired electron as it is a d9 ion after losing two electrons.
3. Ca has no unpaired electrons as it is an s2 element.
4. Cr³⁺ has 3 unpaired electrons. It starts as a d5 ion after losing three electrons.
5. Ni²⁺ has 2 unpaired electrons.
6. Fe³⁺ is a d5 ion with 5 unpaired electrons.
7. O²⁻ has 2 unpaired electrons since oxygen starts with 2 unpaired electrons and upon gaining 2 electrons (to form O²⁻), these go into the empty 2p orbitals.

Based on the unpaired electrons' counts given, the pair with the same number of unpaired electrons is D) Fe³⁺ and O²⁻.