Classify the following substances into elements, compounds, and mixture.
Mercury, sulfur, sugar, water, sand, gold, coal, oxygen, and alcohol.

Hint: An element is defined as a pure substance that contains only one kind of particle. Compounds are those pure substances that have more than one kind of element or atoms. A material that contains two or more substances either elements or compounds in any ratio is called a mixture.

Complete step by step answer:
-Earlier an element was defined as the simplest form of a pure substance that has a decided physical and chemical property and which can neither be split into nor built from simple substances by any chemical or physical method.
-The modified definition of the element is: An element is a pure substance that has only one kind of particle. These particles are atoms.
-Compounds are those pure substances that have more than one kind of element or atoms.
-A compound is a pure substance that contains two or more than two elements combined in a fixed proportion by mass and which can be converted into its constituent elements by suitable chemical or physical methods. The properties of a compound are completely different from the properties of the elements from which it is made. A material that contains two or more substances either elements or compounds in any ratio is called a mixture. The properties of a mixture have the same properties as their constituents.
-So mercury is a single atom (Hg) so it is an element.
-Sulfur is a single atom (S) so it is an element.
-Sugar, there are three elements in sugar: carbon, hydrogen, and oxygen, so it is a compound.
-Water is made up of 2 elements: hydrogen and oxygen, so it is a compound.
-Sand is made up of more than one compound so it is a mixture.
-Gold is a single atom (Au) so it is an element.
-Coal is made up of more than one compound so it is a mixture.
-Oxygen is a single atom (O) so it is an element.
-Alcohol is made up of carbon, hydrogen, and oxygen so it is a compound.

Note: Metals, non-metals, and metalloids are the classification of elements. Compounds are two types: organic compound and an inorganic compound. Homogeneous mixture and heterogeneous mixture are the classification of mixture.