Answer:
1) Dependent variable: Type of separation method used
Independent variables: Substance that separated out
Constants: Sand, pepper, and salt
2) you can use the properties of matter to decide on a method to separate out a particular substance based on its unique properties. For example, knowing pepper has a very small mass allows you to use the charge of the static electricity to separate out those particles. Additionally, knowing the solubility of salt allows you to add water to the mixture to be able to remove it from the sand, since the salt dissolves in the water which is poured away.