Explanation:

- Inert gases (Option 2) are elements in group zero. They are also known as noble gases. They have complete outer shells, making them very stable and unreactive.

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- Reactive (Option 1) refers to elements or substances that readily engage in chemical reactions. Group zero elements are not reactive.

- Radioactive (Option 3) pertains to elements with unstable nuclei. Noble gases are generally not radioactive.

- Volatile (Option 4) describes substances that easily evaporate. While some noble gases can be volatile, this term doesn't define the group.

Your selected answer is correctly identifying the group zero elements as inert gases.