Hello, How do you know which isotope is the most abundant?

How do you know which isotope of an element is the most stable?

Also, How do you know which isotope of an element is the most radioactive?

Calculate the average atomic mass of chlorine if its isotopes and % abundances are as follows.  Show all work.
Chlorine-37      24.23 % abundant      36.9659 amu
Chlorine-35      75.77 % abundant      34.9689 amu


   •   Bromine has two naturally occurring isotopes, 79Br & 81Br. If the weighted average atomic mass on the periodic table is 79.90, what can you say about the relative abundances of each isotope?




   •   Silicon has three naturally occurring isotopes; silicon-28, silicon-29, and silicon-30.
   •   If the weighted average atomic mass on the periodic table is 28.09, what is the most abundant isotope?

   •   How do you know this?
            

Most stable isotope is the most abundant isotope( one with largest percent abundance).

To calculate average atomic mass of Cl = ( 24.23 % x 36.9659 amu +  75.77 % x   34.9689 amu )/ 100


Weighted average is nearly in between 79 and 81  so it means the percent abundance is nearly same for them.

weighted average atomic mass of Si on the periodic table is 28.09 so it means Si-28 is most abundant.

The weighted average atomic mass is always more closer to the most abundant isotope.