The compound k2o2 also exists. A chemist can determine the mass of k in a sample of known mass that consists of either pure k2o or pure k2o2 . From this information

the answers would be

the first one and the second one

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.