Final answer:
To calculate the isotopic mass of the least abundant isotope, you can use the formula for calculating average atomic mass. Plug in the values given and calculate. The answer is 123.574 u.
Step-by-step explanation:
To calculate the isotopic mass of the least abundant isotope, we can use the formula for calculating average atomic mass. The formula is:
Average atomic mass = (mass of isotope 1 * abundance of isotope 1) + (mass of isotope 2 * abundance of isotope 2) + ...
Given that the most abundant isotope has an isotopic mass of 121.814 u and a relative abundance of 67.81%, we can plug in the values:
Average atomic mass = (121.814 u * 67.81%) + (mass of least abundant isotope * abundance of least abundant isotope)
Solving for the mass of the least abundant isotope, we get:
mass of least abundant isotope = (average atomic mass - (121.814 u * 67.81%)) / (abundance of least abundant isotope)
Substituting the given average atomic mass of 122.244 u and abundance of the least abundant isotope, we get:
mass of least abundant isotope = (122.244 u - (121.814 u * 67.81%)) / (100% - 67.81%)
Calculating this equation will give us the isotopic mass of the least abundant isotope.
Therefore, the correct answer is A. 123.574 u.