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

The correct answer is "a reaction that releases energy into the environment".

On the basis of energy, the chemical reactions can be of two types exothermic reaction and endothermic reaction.

Exothermic reactions are those reactions in which energy is released in the environment. The energy might release in the form of heat, electricity, sound or light.

For example, the burning of fossil fuels, neutralization reaction, nuclear fission, respiration, the reaction between water and calcium chloride etc.

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In contrasts, endothermic reactions are those in which heat is supplied to the system.

For example, →

it creates acid rain

that scientist would be robert hooke