Naturally occurring lithium consists of 90% \( ^7_3Li \text{ and 10% } ^6_3 Li. \) What is the relative atomic mass of lithium?
- 6
- 6.8
-
6.9
- 7
- 7.1
The correct answer is: C
Explanation
the relative atomic mass of lithium = percentage abundance times the mass number of the first isotope + percentage abundance times the mass number of the second isotope.
the relative atomic mass of lithium = ( \(\frac{90}{100} \times7 + \frac{10}{100} \times 6\)) =(( 0.9 x 7) + (0.1 x 6)) = 6.3 + 0.6 = 6.9.