A mystery element, called "muriaticum" by its discoverer, exist on earth as a mixture of two isotopes. The most abundant isotope (75.76%) has a mass of 34.9689 amu; calculate the average atomic mass and identify the element by its modern name

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Radon-222 or rn-222 has a half-life of 3.82 days. to determine the fraction of an original sample of rn-222 that remains unchanged after 7.646 days, we calculate the amount of rn-222 remaining after 7.646 days and divide it with the original amount. using 1 gram as a basis and using half-life calculation methods, we can determine that  0.249 or 0.25  grams of rn-222 will remain, and thus the fraction remaining is 0.25 or 1/4.