A student is given a sample of matter and asked to determine whether it is an element, compound, or mixture. The student discovers that she cannot separate the components of the sample by physical means. However, she is able to separate the sample by chemical means into three different pure substances. The
sample must be.

A. an element
B. a compound
C. a mixture
D. a solution

Answer is B

A mixture means two compounds mixed together but not atomically. For example, sand and water solution. A water with sand mixed inside is a mixture because the sand can be separated by physical means.

Water is H2O. This means it is a compound, because hydrogen and oxygen is bonded together atomically. Hydrogen however is an element, because you can't seperate it anymore (You could seperate it in the sense of protons and neutrons, but the definition of element is something you can see on the periodic table)

Compound means more than one element bonded together.

The sample must be a compound because it couldn't be seperated by physical means but can be seperated by chemical means into three pure substances (synonym of element)

nacl or sodium chloride is an ionic compound. this is because an ionic compound pertains to a compound that consists of positively and negatively charged ions. in this case, na (sodium) has a tendency to lose one electron when it reacts with with other atoms, so the resulting sodium ion contains 11 protons and 10 electrons, thus making it positively charged (na+), when chlorine reacts, it usually gains one electron to form an ion called chloride, thus making it negatively charged ( since the ions are oppositely charged, they attract.