Under high voltages, what property does air exhibit when conductors are separated?

When conductors are separated by air under high voltages, the air primarily acts as an insulator. This is because, under normal conditions, air does not allow electrical current to flow through easily. Instead, it resists the flow of charge, preventing current from passing between the separated conductors.

The property of air as an insulator remains true up to a certain voltage threshold, beyond which it can suffer breakdown and allow current to pass – a phenomenon known as electrical breakdown or arcing. However, in the context of the question, when it comes to typical conditions where conductors are not close enough to cause a breakdown, air consistently functions as an insulator.

In contrast, a conductor would allow electricity to flow freely, which is not the case here. A transformer is an electrical device used to transfer electrical energy between circuits through electromagnetic induction, which does not apply to the characteristic behavior of air under high voltage between separated conductors. Therefore, the correct characterization of air in this context is that of an insulator.