Answer :
Final answer:
After 3 minutes from 4:58 pm to 5:01 pm, considering sodium-25's half-life of 60 seconds, the remaining mass of sodium-25 that was placed in the reaction vessel at 5:01 pm would be 1.25 mg.
Explanation:
The question pertains to the decay of the radioactive isotope sodium-25 and its remaining quantity after a certain period of time. Sodium-25 has a half-life of 60 seconds, which means half of it decays every minute.
Given that at 4:58 pm there was 5.0 mg of sodium-25, we need to calculate how much would remain after 3 minutes (from 4:58 pm to 5:01 pm).
After one half-life (one minute), the quantity would halve from 5.0 mg to 2.5 mg. After two minutes (another half-life), it would halve again to 1.25 mg.
There is no third half-life completed by 5:01 pm, so the mass of sodium-25 placed in the reaction vessel at 5:01 pm would be 1.25 mg.
