What is typically a hallmark of endothermic reactions in terms of energy transfer?

Endothermic reactions are characterized by the absorption of heat from their surroundings, which leads to an increase in the internal energy of the system. As these reactions take in energy, they result in the storage of energy within the chemical bonds of the products formed. This is why the choice indicating that stored energy increases is appropriate; during an endothermic reaction, the reactants absorb energy, which is then stored in the form of chemical potential energy in the products.

In contrast, other options may not accurately reflect the nature of endothermic reactions. For instance, the decrease in entropy, typically associated with a more ordered state, does not capture the essence of energy absorption. While endothermic reactions can influence temperature depending on the system, the increase in temperature is not a defining characteristic, as it can vary based on the environment. Additionally, the formation of bonds often pertains to exothermic reactions rather than endothermic ones. Thus, the hallmark of these processes is indeed the increase in stored energy as reactants absorb heat to transform into products.