What is the atomic mass of chlorine? 

35.5

The correct answer is option 2. 35.5. 

The atomic mass of an element is a weighted average of the masses of all its naturally occurring isotopes, taking into account their relative abundances in nature. For chlorine, there are two stable isotopes: chlorine-35 (\(^{35}\)Cl) and chlorine-37 (\(^{37}\)Cl).

The atomic mass of chlorine is approximately 35.5 atomic mass units (amu). This value represents the weighted average of the masses of chlorine-35 and chlorine-37, considering their relative abundances in nature.