If you have one kilogram of radionuclide, how much will remain after one half-life has passed?

If we start with 1 kg or 1000 g of radionuclide, after one half-life has passed, one-half of the original amount of radionuclide will remain. Therefore, 500 g of the radionuclide will remain. The half-life is the time it takes for a radioactive substance to decay to half its initial amount.