Question

which reaction is exothermic?
a reaction that absorbs energy from the environment
a reaction that requires an activation energy
a reaction that releases energy into the environment
a reaction that does not involve a change in energy

Explanation:

An exothermic reaction is defined as a reaction that releases energy into the environment in the form of heat or light. Reactions that absorb energy are endothermic. All chemical reactions require activation energy, but that doesn't define exothermicity. A reaction with no energy change is not possible according to the laws of thermodynamics.

Answer:

a reaction that releases energy into the environment