Final answer:
Sterile water is used as a preliminary hood cleaning agent because it is free from microorganisms and contaminants, making it suitable for cleaning in a controlled environment such as a laboratory hood.
Step-by-step explanation:
Sterile water is used as a preliminary hood cleaning agent because it is free from microorganisms and contaminants, making it suitable for cleaning in a controlled environment such as a laboratory hood. It helps to remove dust particles and residue from the hood without introducing any foreign substances that could potentially contaminate the working area.