Final answer:
The correct option is D). The average atomic mass of thallium is calculated by using the relative abundances and molar masses of its isotopes, which results in an average atomic mass of approximately 204.19 g/mol. None of the provided options exactly match this, but the closest is 203.88 g/mol.
Step-by-step explanation:
To calculate the average atomic mass of thallium, we take into account the relative abundances and molar masses of its isotopes, Thallium-203 and Thallium-205. As Thallium-203 has a molar mass of 202.75 g and a relative abundance of 29.3%, while Thallium-205 has a molar mass of 204.79 g and a relative abundance of 70.7% (since the total abundance must be 100%), we can use this information to calculate the average atomic mass.
The calculation is as follows:
(0.293 × 202.75 g) + (0.707 × 204.79 g) = 59.406 + 144.786 = 204.192 g/mol
Round this to two decimal places, as we often do with atomic masses, the average atomic mass of thallium is approximately 204.19 g/mol. Among the given options, none exactly match this calculated value. However, the closest option would be D, which is 203.88 g/mol.