[HitCode337]

 I am having trouble classifying them, the following classifications I need to use is element, compound, mixture (homogeneous or heterogeneous mixture).
I don't want the answer but a brief/detailed/easy to understand method on how I can classify them.

1 .Water
2.Carbon
3. Air
4. Table salt
5. Sugar dissolved in water
6. Oxygen
7. Sand in water
8. Soil
10. Chocolate chip cookie

[heretosucceed]

An element entails an entity which is purely made up of one single atom. In the examples you have given us, carbon would be an element as it is purely made up of carbon atoms.

A compound is something which contains more than one atom, but what sets it apart from a mixture is that a compound can be split into its atoms using physical methods, where as to split the atoms in a mixture, most often than not, chemical methods are applied.

A compound then in your case would be, sand in water. A mixture would be soil.

[Borek]

A compound is something which contains more than one atom, but what sets it apart from a mixture is that a compound can be split into its atoms using physical methods, where as to split the atoms in a mixture, most often than not, chemical methods are applied.

You got it reversed.

[Jzalkm]

may be helpful to remember that elements and compounds are pure substances made up of a single 'entity' if i may call it such. (an entity would be a single atom, or two or more atoms chemically combined together either by sharing (covalent) or transfer of electrons (ionic).)