4. When a calcium sulfate solution and a barium chloride solution are mixed,a solid forms and settles to the bottom of the mixture. This solid material is called a precipitate reaction catalyst gas

## Step 1<br />The problem describes a chemical reaction where a calcium sulfate solution and a barium chloride solution are mixed. This results in the formation of a solid that settles at the bottom of the mixture. This solid is known as a precipitate.<br /><br />## Step 2<br />A precipitate is a solid that forms in a solution during a chemical reaction. In this case, the solid that forms is a result of the reaction between calcium sulfate and barium chloride.<br /><br />## Step 3<br />The other options provided, such as reaction, catalyst, and gas, do not accurately describe the solid that forms in this scenario. A reaction refers to the overall process of chemical change, a catalyst is a substance that speeds up a chemical reaction without being consumed in the process, and a gas is a state of matter.