Lithium has two naturally occurring isotopes, 6 Li and 7 Li . The average atomic mass of lithium is 6.941. Which of the following statements concerning the relative abundance of each isotope is correct ? A) The abundance of 7 Li is greater than 6 Li. B) The abundance of 7 Li is less than 6 Li. C) The abundance of 6 Li is equal to the abundance of 7 Li. D) Not enough data is provided to determine the correct answer. E) Based on the atomic mass, only 7 Li occurs naturally.