Name one element, one compound and one mixture.

Hint: We know that elements are made up of only one type of atom, compounds are made up of two types of atoms and on the other hand Mixtures contain several elements. Here we can see a correlation between atoms, elements, compounds and mixtures as atoms combine to form an element. On the other hand, at least two elements combine to form a compound whereas several elements or compounds combine to form a mixture.

 Complete answer:
First let us see what is the meaning of each term in detail: -
Element- An element is the substance which cannot be broken down into simpler substances by any chemical process. It is made up of any one kind of atom.
Example: $Cu,Fe,Ag,Al$ etc.

Compound: A compound is a substance which consists of at least two elements. These elements are chemically bound together. A pure compound is always homogeneous. Here homogenous means the same. So, it will contain the same type of elements.

       Example: $C{O_2}$ containing one carbon and two oxygen
                         ${H_2}O$ containing two hydrogen and one oxygen
                         ${H_2}S{O_4}$ containing one Sulphur, two hydrogen and four oxygen

Mixture: A mixture is a substance which is made up of two or more elements or compounds which are physically mixed. They are not chemically bonded together so they can be separated easily by physical method. They are always heterogeneous in nature. Here hetero means different.
Example: Chalk $ + $ water, sand $ + $ water, air

So, one element, one compound and one mixture are
Element: Hydrogen
Compound: Water
Mixture: Air

Note:In a mixture the individual property of each element is retained as they are not chemically bonded together whereas in compounds the atoms lose their individual property after the elements combine chemically to form a compound and thus show only one particular property of the compound as a whole.