chlorine has two isotopes chlorine-35 and chlorine-37 with average atomic mass 35.5.find the percentage abundance of each isotopes

75% Cl-35 and 25% Cl-37

Explanation:

chlorine has two isotopes chlorine-35 and chlorine-37 with average atomic mass 35.5.find the percentage abundance of each isotopes

assume Cl-35 has Y%  Then Cl-37 has (100-Y) %

The weighted average of 35.5 is given by

[(35 x Y) + ((100-Y) x 37)]/100 = 35.5

so

(35 x Y) + ((100-Y) x 37) =3550

35Y + 3700 -37Y =  3550

-2Y = -15075% Cl-35 and 25% Cl-37

Y = so average weight chlorine is

75% Cl-35 and 25% Cl-37