Test Index

WAEC Chemistry 2023 Paper

Question : 36

Total: 50

An element

X

^{65}_{30}\mathrm{X}

^{66}_{30}\mathrm{X}

60\%

40\%

X

Solution:

Isotope

^{65}_{30}\mathrm{X}

(with a mass of 65 and an abundance of

60\%

Relative mass contribution

=(65 \times 60\%)=39.00

Isotope

^{66}_{30}\mathrm{X}

(with a mass of 66 and an abundance of

40\%

Relative mass contribution

=(66 \times 40\%)=26.40

Now, add the relative mass contributions of both isotopes:

Relative atomic mass

A_{r}=39.00+26.40=65.40

So, the relative atomic mass of element X is 65.40 . The correct option is:

65.40

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