the element boron has two naturally occurring isotopes with masses of 10.01amu and 11.01amu. What is the percent abundance of the first isotope.

Answer 1

You have to know the average atomic mass of boron....look at the periodic table to get that.

Now, the math...

avgatomicmass*100=10.01*P + 11.01*(100-P)

solve for P.

Answer 2

10.81 amu