Why is mercury difficult for us to see in its atomic form under normal conditions?

• A. Mercury atoms are always bound in molecules and never exist as free atoms.
• B. Mercury atoms emit light only in the infrared region, making them invisible to the human eye.
• C. Mercury atoms are too small to be resolved by visible light microscopes.
• D. Mercury atoms are transparent to visible light and do not interact with it.

Answer: (C)

Verified step by step guidance

1. Understand that the question is about the visibility of mercury atoms in their atomic form under normal conditions, which relates to how atoms interact with light and how we observe them.
2. Recall that individual atoms, including mercury atoms, are extremely small—on the order of angstroms (10^{-10} meters)—which is much smaller than the wavelength of visible light (about 400-700 nm).
3. Recognize that because atoms are smaller than the wavelength of visible light, visible light microscopes cannot resolve individual atoms; this is a fundamental limit due to the diffraction limit of light.
4. Consider that mercury atoms do exist as free atoms in the vapor phase at high temperatures, but under normal conditions, mercury is a liquid metal where atoms are closely packed, not isolated free atoms.
5. Conclude that the main reason mercury atoms are difficult to see individually under normal conditions is that their size is too small to be resolved by visible light microscopes, making them effectively invisible to the naked eye or standard optical instruments.