The half-life of the radioactive isotope phosphorus-32 is 14.3 days how many days required to loss75% of its radioactivity

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The half-life of the radioactive isotope 137Cs is 30.17 years. How long does one have to wait until exactly 3% of the initial amount of this isotope remains? O A. 200.4 years O B. 140.1 years O C. 152.6 years O D. 29.26 years O E. 170.3 years

The first-order decay of iron-59 has a half-life of 44,495 days. How many grams of iron-59 decompose after one month (assume it is in April) if the sample initially weighs 100.0 g?

The half life for the radioactive decay of potassium-40 to argon-40 is 1.26 x 10 years. Suppose nuclear chemical analysis shows that there is 0.280 mmol of argon-40 for every 1.000 mmol of potassium-40 in a certain sample of rock. Calculate the age of the rock. Round your answer to 2 significant digits. |years

please answer all as they are part of 1 question but different questions,,.

Fallout from nuclear weapons tests in the atmosphere is mainly 90Sr and 137Cs , which have 28.6- and 32.2-y half-lives, respectively. Atmospheric tests were terminated in most countries in 1963, although China only did so in 1980. It has been found that environmental activities of these two isotopes are decreasing faster than their half-lives. Why might this be?