Substance $\mathrm{A}$ decomposes faster on heating in the presence of substance $\mathrm{B}$, whereas substance $\mathrm{B}$ does not undergo any chemical change. What do we call substance $\mathrm{B}$ here? What is the role of these types of substances in chemical reactions?

Write ‘$\mathrm{R}$’ for the substance which undergoes a chemical change and ‘$\mathrm{P}$’ for the new substance which is formed in the following changes.

Write ‘$\mathrm{R}$’ for the substance which undergoes a chemical change and ‘$\mathrm{P}$’ for the new substance which is formed in the following changes.

Write ‘$\mathrm{R}$’ for the substance which undergoes a chemical change and ‘$\mathrm{P}$’ for the new substance which is formed in the following changes.