A scientist experiments on an unknown solution. She notices that when a base, sodium hydroxide, is added to the solution, it forms a salt and water. What can she infer from this observation?

Generally, when an acid and a base are added together in solution, a salt and water will form. This is known as an acid-base reaction. Therefore, the scientist may infer that she is working with an acid. (Acid + Base = H2O + Salt).

She can infer from the observation that the unknown solution is acidic.

To add, acidic solutions are any solution that has a higher concentration of hydrogen ions than water; solutions that have a lower concentration of hydrogen ions than water are called basic or alkaline solutions.