In the scenario you described, where atoms of one element lose an electron and atoms of another element gain an electron, the most appropriate pair from your options would be an alkali metal and a halogen.
Here's why:
- Alkali metals (such as sodium or potassium) have one electron in their outer shell and readily lose that electron to achieve a stable electron configuration, typically resembling that of a noble gas.
- Halogens (such as chlorine or fluorine) have seven electrons in their outer shell and readily gain an electron to also achieve a stable electron configuration, again resembling that of a noble gas.
In this reaction, the alkali metal donates an electron to the halogen, resulting in the formation of ionic bonds and compounds such as sodium chloride (NaCl).
The other options are not suitable for this scenario:
- A halogen and noble gas: Noble gases are already stable and do not gain or lose electrons.
- Two halogens: Both halogens tend to gain electrons; they do not lose electrons in such a reaction.
- Two alkaline earth metals: Alkaline earth metals do lose electrons, but they do not typically gain electrons from each other; they also tend to form cations.
Therefore, the correct answer is an alkali metal and a halogen.