Question

H3PO4 RETARDS THE DECOMPOSITION OF H2O2,THEREFORE IT IS A

Answer 1

The answer is that it act as a negative catalyst .That is phosphoric acid retards the decomposition of H2O2 therefore it is a negative catalyst .  Negative catalysts or inhibitors are those substances which slow down the chemical reactions by decreasing the required activation energy for the reaction, for example the decomposition of Hydrogen peroxide may be slow down by adding a small amount of phosphoric acid in it.