Final answer:
To optimize air flow in a chemical fume hood, opening the sash is the correct action, allowing for proper air currents to remove harmful vapors effectively.
Step-by-step explanation:
To optimize the flow of air in a chemical fume hood, the correct action is a) Opening the sash. The sash is a movable component that acts as a protective shield for the user while also influencing the air flow within the fume hood. When the sash is open, it allows for the creation of proper air currents that are necessary to remove harmful vapors and fumes effectively. It's important to adjust the sash to an appropriate height recommended by the fume hood manufacturer for optimal performance and safety.