Question

which one of the following is the smallest unit of matter that has all the properties of an element? multiple choice electron proton atom compound molecule

Explanation:

• An electron is a subatomic particle with negative charge, not the smallest unit of an element (as it doesn't have the element's properties alone).
• A proton is a subatomic particle with positive charge, also not the smallest unit of an element (lacks the element's properties by itself).
• An atom is the smallest unit of matter that retains all the chemical properties of an element. For example, a single carbon atom has all the properties of carbon.
• A compound is a substance made of two or more different elements chemically bonded, so it's not a unit of a single element.
• A molecule can be of an element (like $O_2$) or a compound, but a single atom of an element (e.g., Ne atom) is the smallest unit with the element's properties, while a molecule of an element is made of multiple atoms.

Answer:

C. atom