Answers

2015-09-04T16:19:05+05:30
Let the abundance of isotope of mass 70 be x %.
abundance of isotope of mass 74 = (100- x) %.

atomic weight =  \frac{70 \times x+ (100-x) \times 74}{100}

\Rightarrow 71 =  \frac{70x+ 7400 - 74x}{100}\\ \\ \Rightarrow 7100 =  70x+ 7400 - 74x\\ \\\Rightarrow -4x = -300\\ \\\Rightarrow x = 75

Abundance of isotope with mass 70 is 75% and abundance of isotope with mass 74 is 25% .
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