Penikill'em which is stored in the refrigerator and has a molecular weight of 450 g/mol or azithrolyse"em which is stored at room trmperature and has a molecular weight of 200 g/mol which drug will you choose

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.

yes the answer is total mass in unchanged   : )