Atomic Weight is the average weight of all naturally occurring forms of the element.

• A. Buffer
• B. Solute
• C. Atomic Number
• D. Atomic Weight

Answer: (D)

Atomic weight is the weighted average mass of an element’s naturally occurring isotopes, accounting for how abundant each isotope is. In nature, elements exist in multiple isotopes with different masses, so the overall mass value reflects the mix of these forms. For example, chlorine has two common isotopes with masses near 35 and 37, and their natural abundances combine to give an atomic weight of about 35.45 amu. This concept distinguishes atomic weight from other terms: a buffer or solute are components related to solutions, not to an element’s mass; the atomic number is the count of protons, which defines identity rather than an average mass. Atomic weight is the phrase that describes this average mass across natural isotopes.