The type of reaction where a more complex compound breaks down into two or more simpler substances is called a decomposition reaction.

Quick Scoop

  • In a decomposition reaction, a single compound (often written as ABABAB) breaks apart into simpler substances (A+BA+BA+B or more).
  • It is the opposite of a combination (synthesis) reaction, where simpler substances join to form a more complex compound.
  • Example: When calcium carbonate is heated, it decomposes into calcium oxide and carbon dioxide:
    CaCO3→CaO+CO2\text{CaCO}_3\rightarrow \text{CaO}+\text{CO}_2CaCO3​→CaO+CO2​.

So, the answer to: “In which type of reaction does a more complex compound break down into two simpler substances?”
is: Decomposition reaction.

TL;DR: A more complex compound breaking down into simpler substances is undergoing a decomposition reaction.

Information gathered from public forums or data available on the internet and portrayed here.