A 400-mg sample of technetium-99m is used for a diagnostic test. If technetium-99m has an effective half-life of 4.8 hours, how much of the technetium-99m remains 72 hours after the test?
Express your answer to two significant figures and include the appropriate units.

16. why must the number of electrons lost equal the number of electrons gained in every redox reaction? use 3 – 4 sentences in your own words to address this question. 18. what type of radiation is emitted when chromium-51 decays into manganese-51? show the nuclear equation that leads you to this answer. 19. a radioactive nucleus alpha decays to yield a sodium-24 nucleus in 14.8 hours. what was the identity of the original nucleus? show the nuclear equation that leads you to this answer.