Half-life is the time needed for half the nuclei of a radioactive sample to decay; it is unique to each isotope and independent of external factors.
The correct definition for the term ‘half-life’ is neither A, B, C, nor D, but rather it can be better defined as the time required for half of a radioactive element to lose half of its radioactivity. Specifically, half-life is the period of time after which half of a substance’s original nuclei will have decayed. For instance, Carbon-14, which is used in radiocarbon dating, has a half-life of approximately 5700 years. Another example is Uranium-234, with a half-life significantly longer, calculated at 245,000 years. It’s important to note that each radioactive isotope has its unique half-life independent of external factors such as temperature or concentration changes, and this property is a key part of understanding radioactive decay.