She measured 5.0 kg of substances x at noon Tuesday shaunameasured 1.25 kg of substance x what is the half- life of substance x?

Answer 1

If substance x decays by emitting 100% gas which escapes leaving no residues, then the half-life is half the time elapsed since noon Tuesday

If substance x contains some components which decay by say, K capture (the nucleus captures one of its orbiting electrons) with practically no change in mass, then the picture is complicated because it may have a short half-life, not detectable by weighing.

For this reason half-life is not determined or defined by weight. It is defined by the proportion of the original atomic species which remains after some interval of time, possibly determined by, say, chemical or spectroscopic analysis.

Answer 2

The half-life of substance X can be calculated based on the ratio of the measured amounts. If 5.0 kg reduces to 1.25 kg, this represents one half-life as the amount is halved. Therefore, the half-life of substance X is the time between noon Tuesday and when Shauna measured 1.25 kg of substance X.