Which of the following is the atomic mass of fluorine?

• A. 20.00 u
• B. 19.00 u
• C. 9.00 u
• D. 18.99 u

Answer: (B)

Verified step by step guidance

1. Understand that the atomic mass of an element is the weighted average mass of all its naturally occurring isotopes, measured in atomic mass units (u).
2. Recall that fluorine has only one stable isotope, fluorine-19, which means its atomic mass is very close to 19 u.
3. Compare the given options to the known atomic mass of fluorine, which is approximately 18.998 u, often rounded to 19.00 u.
4. Eliminate options that are significantly different from 19 u, such as 20.00 u and 9.00 u, since they do not match the known atomic mass of fluorine.
5. Select the option closest to the known atomic mass, which is 19.00 u or 18.99 u, noting that 19.00 u is the commonly accepted rounded value.