3) Rn-222 is the most stable isotope of radon. If it takes 9.74 days for a sample of Rn-222 to decay to 17%
of its initial mass, what is the half-life of Rn-222?

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.