Giving an example lists two information which makes a chemical equation more useful.

Hint: Different kinds of information we generally get from the equation and most important the two which have to be there are the physical state of the system that is whether solid, liquid or gas, then comes the gas evolution that means whether the gas is evolved or not in the reaction.

Complete answer:
When we talk about the chemical equation we must remember that whenever the chemical reaction takes place then the two or more compounds we come to know that it is represented in short by writing the chemical equation. So, we can say that if we want to know what happens at the end of the reaction we must see the equation so from this we conclude that the equation must include all the information. Firstly we will talk about the physical state. as we all know that there are three states that are solid, liquid and gas. In order to get the correct information about the particular compound we must know its state. so if the substance exists in solid state we must write it as (s) in the equation. If the aqueous then we write (aq) and further if the state is gaseous one we write it as (g) in the equation. This can be shown through the example.
\[CaC{O_3}\xrightarrow{{HEAT}}CaO(s) + C{O_2}(g)\]
So then we will move on to the other information that is the evolution of gas.as we know that whenever the reaction takes place then there must be the evolution of some or the other gas. In the chemical equation this evolution is shown through an arrow upward indicated and its physical state shown by (g). this can be further shown through an example:
\[Zn(s) + {H_2}S{O_4}\left( {aq} \right) \to ZnS{O_4}\left( {aq} \right) + {H_{_2}}\left( g \right) \uparrow \]

Note: There is much information shared through the equations and further can be explained as the heat evolved or not in the reaction is further the important aspect to be known. This evolution of heat is further shown by the delta symbol.