What occurs during one half-life?
a. half of a daughter isotope undergoes radioactive decay to form a parent isotope.
b. half of a parent isotope undergoes radioactive decay to form a daughter isotope.
c. all of a daughter isotope undergoes radioactive decay to form a parent isotope.
d. all of a parent isotope undergoes radioactive decay to form a daughter isotope.

 Actually its the parent isotope that undergoes radioactive decay.

So option A and C is not correct.

And in one half life;

what happens is half of the parent isotope decays to form daughter isotopes.

Hence the correct option is B:

B. Half of a parent isotope undergoes radioactive decay to form a daughter isotope.

space exploration has led to the development and technological improvement of many everyday items. (if this answer is wrong i will find the right answer) : )