how is radius of nucleus is proportional to (A^1/3) where A is mass number?
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hope that answer will be appropriate with detail not just an equation!

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Hint: if you assume that mass number is related to the volume of the nucleus, and if you assume that the nucleus is spherical, this comes down to understanding how the volume of a sphere relates to its radius. Can you take it from here? Post back with what you think the explanation is and we'll check it for you.