Answer: The correct answer is a mixture.
Step-by-step explanation:
A compound is defined as the substance which is formed from the combination of two or more different elements in a fixed ratio.
Conserving mass states that mass can neither be created nor be destroyed but it can only be transformed from one form to another. Total mass on the reactant side is equal to the total mass on the product side in a chemical reaction.
An element is defined as the substance which is made from similar kind of atoms. It cannot be divided into simpler substances.
A mixture is defined as combination of two different substances which are not combined in the fixed ratio.
In the question, it is given that a solution is made from 4 grams of salt that is dissolved in 100 grams of water. If some water is evaporated, the salt still remains in the solution, which makes it a mixture of salt and water.
Hence, the correct answer is a mixture.