An element X has isotopic masses of 6 and 7. if the relative abundance is 1 to 12.5 respectively, what is the relative atomic mass of X?

  • A 6.0
  • B 6.1
  • C 6.9
  • D 7.0
waec 2006chemistry

The correct answer is C. 6.9

Contribution by isotope 6 = 6 x 1 = 6

contribution by isotope 7 = 7 x 12.5 = 87.5

This contribution is made by 1 + 12.5 = 13.5 atoms

Relative atomic mass of = 87.5 + 6 = 93.5/13.5 = 6.9

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