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

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

Step-by-step explanation:

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

`((abundance \: * \: mr) \: + \: (abundance \: * \: mr))/(100)`

`((75 * 35) + (25 * 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