Chemists assign atoms to chemical elements by counting their:

• A. number of neutrons
• B. number of electrons
• C. atomic mass
• D. number of protons

Answer: (D)

Verified step by step guidance

1. Understand that atoms are identified by their atomic number, which is the number of protons in the nucleus of the atom.
2. Recognize that the number of protons defines the chemical element because each element has a unique number of protons.
3. Note that the number of neutrons can vary within atoms of the same element, leading to different isotopes, but this does not change the element itself.
4. Understand that the number of electrons can change in ions, but the element identity remains based on protons.
5. Recall that atomic mass is the sum of protons and neutrons and is not used to assign the element, but rather to describe isotopes and atomic weight.