Question

question 1. elements are different because their atoms contain different numbers of _______________. electrons. neutrons. protons. nuclei.

Explanation:

The atomic number, which is determined by the number of protons in an atom's nucleus, defines the element. Different elements have different atomic numbers due to different numbers of protons. Electrons can be lost, gained or shared in chemical reactions and do not solely define an element. Neutrons can vary in number (isotopes) without changing the element. Nuclei are the central part of the atom and the number of nuclei doesn't define the element - it's the protons within the nucleus that matter.

Answer:

protons.