The half-life of a certain element is 100 days. how many half-lives will it be before only one eighth of this elementremains?

b) mutualism

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since the atomic number is the number of protons in the nucleus, as we move to the left on the periodic table, the electrostatic pull between the nucleus and the valence electron shell decreases. as we move down a group (vertical column), the valence shell energy level gets further and further from the nucleus.

10 years is the answer

6.4 cm (max) - 25 cm (min)