Where two liquid substances are mixed together and a solid forms by a chemical reaction, the solid is known as what?

Is it heterogeneous mixture?

The fact that paper burns and turns into different substances is known as ____ ____of paper?
I honestly am unsure of this answer, at first i thought something to do with gaseous state, but not sure.

The solid is a precipitate.

Paper burns by a process called combustion. I realize that is one word and your post makes it appear to be two words.

When two liquid substances are mixed together and a solid forms by a chemical reaction, the solid product is known as a precipitate. A precipitate is a solid that forms when two or more liquids react chemically, resulting in the formation of an insoluble solid. This solid can be filtered or separated from the remaining liquid mixture.

Regarding the fact that paper burns and turns into different substances, it is not related to the gaseous state. The process of paper burning and turning into different substances is known as combustion. Combustion is a chemical reaction in which a substance reacts with oxygen, typically producing heat, light, and new chemical compounds. In the case of paper burning, it undergoes a combustion reaction, transforming the paper into ash, gases such as carbon dioxide and water vapor, and potentially other byproducts.