Sodium-25 is to be used in an experiment in our lab. If 5.0 mg of sodium-25 was removed from the reactor at 4:58 PM, exactly how many mg of the isotope was placed in our reaction vessel in the laboratory at 5:01 PM? The half-life of sodium-25 is 60 seconds.

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.