Final answer:
The average atomic mass of rubidium, when calculated by taking into account the abundance and mass of its isotopes, is approximately 85.6 amu. The closest given option is b) 86.2 amu.
Step-by-step explanation:
To calculate the average atomic mass of rubidium, which has two isotopes, rubidium-85 and rubidium-87, we need to multiply the mass of each isotope by its relative abundance and then sum the results. The mass of rubidium-85 is 85 amu with an abundance of 72.2%, and the mass of rubidium-87 is 87 amu with an abundance of 27.8%.
The calculation would be as follows:
- (85 amu × 0.722) + (87 amu × 0.278) = 85 amu × 0.722 + 87 amu × 0.278 = 61.37 amu + 24.186 amu = 85.556 amu.
When rounded to one decimal place, the average atomic mass of rubidium is 85.6 amu, which is not exactly presented in the multiple-choice options provided. However, if we are to choose the closest answer, it would be option b) 86.2 amu.