we cannot specify how long an individual radioactive isotope will survive before it decays, but we can measure how long it takes for a population of the parent isotopes to be halved. this is a consequence of half of the parent isotopes decaying into daughter isotopes. this time unit is called the half-life of the isotope. for a given radioactive element, the half-life is a constant regardless of conditions. q19 the ratio of parent-to-daughter isotopes changes with the passage of each successive half-life. how many of the original atoms of a parent isotope remain unchanged after five half-lives? group of answer choices 1/4 1/8 1/16 1/32