which is a feature of a single - replacement reaction?\nsubstance xyz breaks down into x and yz.\nsubstance…

Explanation:

Step1: Recall single - replacement reaction definition

A single - replacement reaction is a chemical reaction where one element replaces another element in a compound. The general form is $A + BC\rightarrow AC + B$.

Step2: Analyze each option

• Option 1: Substance $XYZ$ breaks down into $X$ and $YZ$ is a decomposition reaction ($AB\rightarrow A + B$), not a single - replacement reaction.
• Option 2: Substance $G$ reacts with compound $XY$ to form $GY$ and $X$. This follows the form $G+XY\rightarrow GY + X$, which is a single - replacement reaction where $G$ replaces $X$ in the compound $XY$.
• Option 3: Substance $X$ burns rapidly in the presence of oxygen is a combustion reaction (usually $X + O_2\rightarrow$ products), not a single - replacement reaction.
• Option 4: Substances $QR$ and $GT$ exchange ions with each other is a double - replacement reaction ($AB+CD\rightarrow AD + CB$), not a single - replacement reaction.

Answer:

Substance $G$ reacts with compound $XY$ to form $GY$ and $X$.