The table below gives the atomic mass and relative abundance values for the three isotopes of element M.Relative abundance (%)Atomic mass (amu)78.9923.985010.0024.985811.0125.9826What is the average atomic mass (in amu) of element M?

Multiply each isotope’s mass by its fractional abundance and add the results: (0.7899 × 23.9850) + (0.1000 × 24.9858) + (0.1101 × 25.9826) ≈ 24.30 amu. The average atomic mass is therefore 24.30 amu, choice C.

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