Answer :
After 90 years amount of Cs-137 isotopes has a half-life of 30 years. would remain is equal to = 0.125 grams.
An important and useful factor of radioactive decay is half of life, which is the amount of time it takes for one half of a radioactive isotope to decay. The half of-life of a selected radioactive isotope is constant; it is unaffected by way of situations and is independent of the initial quantity of that isotope.
The half of life of a chemical reaction can be defined because the time is taken for the awareness of a given reactant to attain 50% of its preliminary awareness. The half of-life of a response is the time required for the reactant's attention to decrease to at least one-half of its initial price. The half of-life of a first-order response is consistent this is associated with the charge consistent for the reaction. t1/2 = 0.693/k
Since all radioactive reaction follows first-order reaction, The rate of reaction does not depend on initial concentration.
calculation:-
1 gram Cs-137 at T = 0
after the first half,
⇒0.5 gram Cs-137 at T = 30
After the second half,
⇒0.25 gram Cs-137 at T = 30.
After the third half,
⇒0.125 gram Cs-137 at T = 90 years.
Hence, after 90 years amount of Cs-137 would remain is equal to = 0.125 grams.
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