Question

one half of barium-139 decays into another element after 86 minutes. the 86 minutes is referred to as this elements...
select one:
○ a. half-life.
○ b. radioactive phase.
○ c. time zone.
○ d. quarter time.

Explanation:

The term defined as the time required for half of a radioactive substance to decay is a standard concept in nuclear science. Among the options, only "half-life" matches this definition. The other options are irrelevant: radioactive phase does not refer to decay time, time zone relates to geographic time offsets, and quarter time is not a term for radioactive decay.

Answer:

a. half-life.