Which of the following is a requirement of a lubricant?

• A. Seal
• B. Color
• C. Viscosity
• D. Odor

Answer: (A)

Lubricants must form a film that separates moving surfaces and stays contained in the system. That containment acts like a seal, keeping the lubricant in place under pressure and blocking contaminants from entering the bearing clearance. This sealing function is fundamental to how a lubricant works in real machinery: if the lubricant leaks away or dirt gets in, wear and damage quickly follow. Color and odor aren’t functional requirements of lubrication—they’re just characteristics that can vary with additives and manufacturing. Viscosity is important for the lubricant’s performance, but the option that best represents a core practical need is the ability to seal the lubricant within the system and prevent leakage and contamination.