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JAMB Chemistry 2019 Paper

Question : 77

Total: 80

{}^{16}_{8}

{}^{18}_{8}

Z. Its relative atomic mass is

Solution:

Concept:

The relative atomic mass is the weighted average of the masses of an element's isotopes, using their percentage abundances as weights.

Explanation:

Isotope

{}^{16}_{8}\mathrm{Z}

has mass number

16

and abundance

80\%

Isotope

{}^{18}_{8}\mathrm{Z}

has mass number

18

and abundance

20\%

Convert percentages to fractions:

80\% = \frac{80}{100}

and

20\% = \frac{20}{100}

Relative atomic mass

= (16 \times \frac{80}{100}) + (18 \times \frac{20}{100})

= (16 \times 0.8) + (18 \times 0.2)

= 12.8 + 3.6

= 16.4

Answer:

\text{D. } 16.4

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