Matter is anything with mass that takes up space.
Mass is the measure of matter in an object.
Sorry I know this is really round about but I couldn't find a better definition.
Next elements and compounds, what's the difference? Well both are pure substances but elements only have one type of atom (the smallest "building block" of everything) while compounds are two or more types of atoms that are chemically bound.
Now another contrast is heterogeneous vs. homogeneous this one is very simple the only real difference is if you can pick apart the solution. (which means mixture) So heterogeneous means it can be pulled apart physically, like a salad. Homogeneous means that cannot be physically separated like sugar water, once it's dissolved you can put it back without using chemical methods.
Acids are acidic which means that they have ph lower than 7 which is the level water has. Acids have a sharp intense flavor nad feel sticky.