Which of the following physical properties is characteristic of helium?

• A. It is a colorless, odorless gas at room temperature.
• B. It is a solid with a metallic luster at room temperature.
• C. It is a highly reactive gas that forms compounds easily.
• D. It is a dense liquid at room temperature.

Answer: (A)

Verified step by step guidance

1. Recall the position of helium on the periodic table: it is a noble gas located in Group 18 (the far right column).
2. Understand the general physical properties of noble gases: they are all gases at room temperature, colorless, odorless, and chemically inert (non-reactive).
3. Analyze each option in the context of helium's known properties: helium is not a solid or liquid at room temperature, nor does it have metallic luster or high reactivity.
4. Recognize that helium remains a gas under standard conditions (room temperature and atmospheric pressure) and does not form compounds easily due to its full valence electron shell.
5. Conclude that the characteristic physical property of helium is that it is a colorless, odorless gas at room temperature.