Answer:is D.the wave theory of light
Explanation:
cuz i got it wrong :( but the answer is correct :3
The atomic mass<span> of an element is a weighted average of its </span>isotopes<span> in which the sum of the abundance of each isotope is equal to 1 or 100%.
</span><span>Let fraction of N-15 be x
then fraction of N-14 = 1-x
</span>
<span>Formula for Calculating Isotope:
</span>

on calculation:
x = <span>0.006403
so, % = 0.006403 x 100 = 0.6403 %<span>
</span></span>