25000 molecules of U-238 element will be left after 4.5 billion years.
Half-life of radioactive elements refers to the time interval needed for one-half of the atomic nuclei of a radioactive sample to decay. The change occurs in the radioactive element into other nuclear species by emitting particles and energy.
Radioactive decay reduces the number of radioactive nuclei up to half of its original value or molecules so we can conclude that 25000 molecules of U-238 element will be left after 4.5 billion years.
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