Explanation:

- Group 18: These are the noble gases, including helium, neon, argon, and others. They are non-reactive due to their full valence shell. They exist as monoatomic gases and have very low boiling points.

- Group 16: Includes oxygen, sulfur, and others, which are reactive. They are not monoatomic in their natural state.

- Group 15: Contains nitrogen, phosphorus, etc. While some elements like nitrogen are gases, they are reactive.

- Group 13: Elements like boron and aluminum are found here. They are generally metals or metalloids.