What percentage of original radiactive atom is left after four half lives:

What percentage of the living species of animals is threatened?

At any instant, the ratio of the amount of radioactive substance is 2:1. If their half lives be respectively 12 and 16 hours, then after two days what will be the ratio of the substances?

True or False : If [A]_0 is the initial concentration of a reactant following first order reaction, then after three half lives its concentration becomes ([A]_0)/3^2 .

The half-life of ._(6)^(14)C is 5730 year. What fraction of its original C^(14) would left after 22920 year of storage?

Half life of a certain radioactive material is 130 days. After what lapse of time, the undecayed fraction of the material will be 25% ?

Half life of a certain radioactive material is 140 days. After what lapse of time, the undecayed fraction of the material will be 25% ?