Final answer:
The atomic mass of antimony, based on its naturally occurring isotopes Sb-121 and Sb-123, is calculated to be 121.7 amu. This value is found by multiplying the isotopic masses by their respective abundances and summing the results.
Step-by-step explanation:
Calculating the atomic mass of an element like antimony (Sb) which has two naturally occurring isotopes can be done using the abundances and masses of its isotopes. The isotopes in question are Sb-121 with a mass of 120.9 amu and an abundance of 57.21%, and Sb-123 with a mass of 122.9 amu and an abundance of 42.79%. To find the average atomic mass, we use the following equation:
Atomic Mass = (Fractional Abundance of Isotope 1 × Mass of Isotope 1) + (Fractional Abundance of Isotope 2 × Mass of Isotope 2)
For Sb-121 and Sb-123, the calculation looks like this:
Atomic Mass = (0.5721 × 120.9 amu) + (0.4279 × 122.9 amu)
Atomic Mass = (69.1 amu) + (52.6 amu)
Atomic Mass = 121.7 amu
The closest answer to our calculated atomic mass of 121.7 amu is option (c) 121.1 amu, but there seems to be a rounding or typing error in options presented. The most accurate calculation based on the provided data leads to an atomic mass not precisely matching the given options.