Question

Chlorine has two isotopes, Cl-35 and Cl-37 with the average atomic mass 35.5. what is the percentage composition of Cl-35 and Cl-37 respectively?
A 25% and 75%
B 75% and 25%
C 65% and 35%
D 35% and 65%​

Answer 1

Answer:

75% of Cl-35 and 25% of Cl-37

Explanation:

Equation to find the mass number of an element. repeat the brackets for however many isotopes it has.

$\frac{(abundance \: \times \: mr) \: + \: (abundance \: \times \: mr)}{100}$

$\frac{(75 \times 35) + (25 \times 37)}{100} = 35.5$

You can try guess it because 35.5 is closer to 35 than 37 so it has a higher abundance of Cl-35