Magnesium has three common isotopes. The masses of the first two isotopes and percent abundances are as follows: 24.1687 amu, 78.900%
25.4830 amu, 10.009%

If the atomic mass of magnesium is 24.305 amu, what is the percent abundance of the
third isotope?
What is its atomic mass?

Explanation:

percentage abundance of third isotope = 100 - ( 78.900 + 10.009)

= 11.091 %

Atomic mass

24.1687 x .789 + 25.4830 x .10009 + 24.305 x .11091  

19.069 + 2.5506 + 2.69566

= 24.3153 amu

when the volume of gas is   changed from   717.73 ml   to 852 ml   the temperature will   change   from 315   c to 452   c

    calculation

this is calculated using the charles law formula

that is,   v1/t1 = v2/t2

          v1=?

        t1 = 315 c   into   kelvin = 315 +273 = 588 k

        v2 = 852   ml

        t2 = 425c + 273 =698 k

make v1   the subject of the formula ( by   multiplying both side by t1)

  v1=( v2 xt1) / t2

v1= (852 ml   x 588 k)/ 698 k= 717.73 ml