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Naturally occurring lithium consists of 90% \( ^7_3Li \te...

Naturally occurring lithium consists of 90% 73Li and 10% 63Li. What is the relative atomic mass of lithium?

A.

6

B.

6.8

C.

6.9

D.

7

E.

7.1

Correct answer is C

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 = ( 90100×7+10100×6) =(( 0.9 x 7) + (0.1 x 6)) = 6.3 + 0.6 = 6.9.