When a substance breaks up into two simpler substances, the reaction
is an)
reaction.

Decomposition.

Explanation:

Decomposition Reactions T hose reactions in which a single substance (reactant) splits up into two or more simpler substances (products) are known as decomposition reactions. These reactions are carried out by supplying energy in form of heat, electricity or light which breaks that substance into simpler substances

while cooking a piece of 1/2 pound beef steak, a cast iron pan (2.4kg in weight) was heated 260 celsius.