Why must the container of the test strips be tightly closed?

The correct answer emphasizes the importance of protecting the reagent on the test strips. Test strips are designed with specific chemical reagents that react to the substances being tested. When the container is not tightly closed, these reagents can be exposed to air and moisture, which can degrade their integrity and effectiveness over time. Even small exposure can result in unreliable test results or a complete failure of the strip to perform as intended.

While other options suggest valid concerns—the prevention of evaporation or contamination from air—they are secondary to the primary need to protect the reagents themselves. A tightly sealed container helps ensure that the test strips retain their functional properties, thus ensuring accurate and reliable results. Maintaining the integrity of the reagents is crucial for the testing process, making this the most significant reason for keeping the container securely closed.