Which of the following sets contains isoelectronic species?Na+ and Cl–K+ and Cl–Ca2+ and F–Mg2+ and Cl–

Isoelectronic species are atoms, ions or molecules that have the same number of electrons. Let's examine each pair:

1. Na+ and Cl–: Sodium ion (Na+) has 10 electrons (since it has lost one electron) and Chloride ion (Cl–) has 18 electrons (since it has gained one electron). So, they are not isoelectronic.

2. K+ and Cl–: Potassium ion (K+) has 18 electrons (since it has lost one electron) and Chloride ion (Cl–) also has 18 electrons. So, they are isoelectronic.

3. Ca2+ and F–: Calcium ion (Ca2+) has 18 electrons (since it has lost two electrons) and Fluoride ion (F–) has 10 electrons (since it has gained one electron). So, they are not isoelectronic.

4. Mg2+ and Cl–: Magnesium ion (Mg2+) has 10 electrons (since it has lost two electrons) and Chloride ion (Cl–) has 18 electrons. So, they are not isoelectronic.

Therefore, the set that contains isoelectronic species is K+ and Cl–.