Final answer:
A catalyst in a chemical equation is denoted by the abbreviation (cat) written above the arrow.
Step-by-step explanation:
A catalyst for a reaction is indicated by a (cat) written over the arrow in a chemical equation. Catalysts are substances that increase the rate of a reaction without being consumed in the process. In a chemical equation, special conditions such as the presence of a catalyst might be designated by writing symbols or abbreviations above or below the equation's arrow. For example, heat is often represented by an uppercase Greek letter delta (Δ) over the arrow, and for catalysts, the abbreviation (cat) is used.
Special conditions necessary for a reaction, like reaction conditions, catalysts, or heat, can be written above or below the arrow. While heat can be indicated by a triangle (Δ) symbol, the formula or abbreviation written over the arrow as a catalyst can vary, with the correct identification for a catalyst being (cat).