Final answer:
A hypotonic solution is more pure compared to the cell's interior because it has a lower concentration of solutes, resulting in water entering the cell.
Step-by-step explanation:
When the solution outside of a cell is hypotonic, it means that this solution has a lower solute concentration compared to the inside of the cell. As a result, the net flow of water will be into the cell through the process of osmosis. Eventually, this can cause the cell to swell and possibly burst, a process known as lysis. Consequently, the correct answer to the question is that a hypotonic solution is (a) pure, as it has less solute compared to the cell's interior.