What percentage of the original parent isotope remains after each of the following half lives have elapsed?

About 50 % of the half life is left form the original isotope in first phase.

Explanation:

As half-life is a time it will take for the radioactive substance to decay like the isotope radiation produced in there atomic mass when they are fused with other substance tends to produce the energy that is needed for the experiment and this energy or life of the substance is the value of the two halves. The ratio goes on like form first 50% life to 25% life than to 12.5% of life and then to 6.25% of life and then to 3.12% of the life remains which is by the one-half, one-quarter, one-eighth, one-sixteenth, one-thirty seconds. This applies based on the radioactive decay of the 1000 isotopes. And most likely you will have 500 left in first life, and rest goes on. Each element has its capacity to give or produce energy.

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