Here's why:

* Catalyst: A catalyst is a substance that speeds up a chemical reaction without being consumed in the process.

* Decomposition of H₂O₂: The decomposition of hydrogen peroxide is a slow reaction that produces water (H₂O) and oxygen gas (O₂):

2 H₂O₂ → 2 H₂O + O₂

* Role of MnO: MnO provides an alternative reaction pathway with a lower activation energy. This means the reaction can happen faster in the presence of MnO.

How it works:

MnO acts as a surface for the reaction to occur. The hydrogen peroxide molecules interact with the MnO surface, facilitating the breaking of the peroxide bond (O-O) and the formation of water and oxygen.

Important Note: MnO is a heterogeneous catalyst, meaning it is in a different phase than the reactants (H₂O₂).