Compared to an atom as a whole, an atomic nucleus is:

• A. much smaller and contains most of the atom's mass
• B. equal in size and mass to the entire atom
• C. much smaller and contains very little of the atom's mass
• D. much larger and contains most of the atom's volume

Answer: (A)

Verified step by step guidance

1. Recall the basic structure of an atom: it consists of a nucleus at the center and electrons surrounding it in a cloud.
2. Understand that the nucleus contains protons and neutrons, which are much heavier than electrons, so most of the atom's mass is concentrated in the nucleus.
3. Recognize that the size of the nucleus is extremely small compared to the overall size of the atom, which is mostly empty space occupied by the electron cloud.
4. Compare the volume and mass: the nucleus is very small in volume but contains nearly all the mass, while the electrons contribute very little to the mass but define the atom's size.
5. Conclude that the nucleus is much smaller than the atom but contains most of its mass.