The time in which half of the given number of radioactive nuclei decay is known as

Explanation

The half life is the interval in which half the undecayed nuclei present decay, and because decay is random with a constant probability per nucleus, that interval stays the same however much material remains. Carbon 14 has a half life of about 5730 years and iodine 131 about 8 days. The quantity is a property of the nuclide and cannot be altered by temperature or pressure.