Answer :
Final answer:
The average atomic mass of chlorine in the sample, given the fractional abundances of Cl-35 and Cl-37, is 35.7 amu, leading to the closest whole number answer B: 35.0.
Explanation:
To calculate the average atomic mass of chlorine when the fractional abundance of Cl-35 is 0.6 (or 60%), and that of Cl-37 must be 0.4 (or 40%) since the two fractions must sum to 1, we use the formula:
average mass = (fraction of Cl-35 × atomic mass of Cl-35) + (fraction of Cl-37 × atomic mass of Cl-37).
Substituting the given values:
average mass = (0.6 × 34.9 amu) + (0.4 × 36.9 amu)
average mass = (20.94 amu) + (14.76 amu)
average mass = 35.7 amu
The answer is rounded to two decimal places following the rules of significant figures, as the atomic weights are given to two decimal places. Thus, the average atomic mass of chlorine in this sample is 35.7 amu, which corresponds to option B: 35.0 when rounded to the nearest whole number.