Which of the following is closest to the atomic mass of bromine (Br)?

• A. 35.45 u
• B. 126.90 u
• C. 63.55 u
• D. 79.90 u

Answer: (D)

Verified step by step guidance

1. Understand that the atomic mass of an element is the weighted average of the masses of its naturally occurring isotopes, measured in atomic mass units (u).
2. Recall that bromine (Br) has two main isotopes: bromine-79 and bromine-81, with approximate natural abundances of about 50% each.
3. Calculate the weighted average atomic mass by multiplying the mass of each isotope by its relative abundance and then summing these values: \(\text{Atomic mass} = (79 \times 0.5) + (81 \times 0.5)\).
4. Perform the addition to find the average atomic mass, which should be close to the known atomic mass of bromine.
5. Compare the calculated average atomic mass to the given options and identify the value closest to your result.