Determine the mass of the second isotope of an unknown element with a weight of 125.8 amu where the other isotope has 51.97% at 125.6 amu using the formula for atomic mass

$\overline{){\mathbf{atomic}}{\mathbf{}}{\mathbf{mass}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}{\left[\mathbf{mass}\mathbf{}\mathbf{\times}\mathbf{}\mathbf{f}\mathbf{.}\mathbf{a}\mathbf{.}\right]}_{\mathbf{}\mathbf{isotope}\mathbf{}\mathbf{1}}{\mathbf{}}{\mathbf{+}}{\left[\mathbf{mass}\mathbf{}\mathbf{\times}\mathbf{}\mathbf{f}\mathbf{.}\mathbf{a}\mathbf{.}\right]}_{\mathbf{}\mathbf{isotope}\mathbf{}\mathbf{2}}}$

where atomic mass = average atomic mass of the element and f.a. = fractional abundance of the isotope. To get ** f.a.**, we simply need to divide the given percent abundance by 100.

An unknown element with atomic weight 125.8 amu has two isotopes. One isotope has an abundance of 51.97% at 125.6 amu. Find the mass of the second isotope.

A. 126

B. 100

C. 148

D. 531

E. Over 9000

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