Chlorine, which exists in nature in two isotopic forms, has an atomic mass of 35.5 amu. This means that:

A. All chlorine atoms have masses of 35.5 amu.
B. The mass of one isotope must be lighter than 35.5 amu while the mass of the other isotope is heavier than 35.5 amu.
C. 35.5 amu is the upper limit for the mass of a chlorine atom.
D. More than half of all chlorine atoms have masses of 35.5 amu.

Chlorine's atomic (1) mass of 35.5 amu represents an average of its isotopes' masses, predominantly chlorine-35 and chlorine-37, not the specific mass of individual chlorine atoms.

Explanation:

The atomic mass of chlorine, 35.5 amu, indicates an average value derived from the weighted average of its isotopes' masses and their relative abundance in nature. Chlorine has two stable isotopes: chlorine-35 and chlorine-37. Their presence in varying proportions around 75.77% and 24.23%, respectively, results in an average atomic mass close to 35.5 amu. This implies that while chlorine-35 atoms are lighter than 35.5 amu, chlorine-37 atoms are heavier.

The atomic mass of 35.5 amu is the weighted average of these isotopes, not an indication that all chlorine atoms possess this specific mass, clarifying the misconception about the uniformity of mass among chlorine atoms.