Eli states that sodium phosphate is a mixture because it is composed of both sodium ions and phosphate ions. Which is the best analysis of Eli’s statement?

It is correct because each ion is a pure substance, so sodium phosphate is made up of two pure substances.
It is correct because the composition of sodium phosphate changes depending on the sample.
It is incorrect because sodium phosphate is a compound that has a single composition.
It is incorrect because the two types of ions in sodium phosphate cannot be seen.