1. The half-life of radioisotope Z is 10 years. If you have 300g of Z, how many grams will be left after 4 decades? 2. How many half-lives would pass if 4000 g of a radioisotope decays into 1000g?

3. The half-life of a radioisotope is 12 minutes. How much time has passed if this radioisotope has gone through 7 half-lives?

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.

im doing test rn im going with 2 but ill give answer if itss wrong,   : )