Which of the following is the most probable cause of a yellow growth on an optical lens?

The presence of a yellow growth on an optical lens is most likely indicative of microbial attack. This phenomenon often occurs when moisture and organic matter are present on the lens surface, creating an environment conducive to the growth of bacteria or fungi. These microbes can produce pigments that appear yellow, leading to the discoloration observed.

While dust accumulation can cause a lens to appear dirty and obscure light transmission, it does not lead to a colored growth. Oxidation refers to the chemical reaction of materials with oxygen, which typically results in surface degradation rather than the development of a colored growth, especially not one that is distinctly yellow. Previous cleaning residue might leave a film or streaks on the lens but would not typically manifest as a yellow growth.

In the context of optical lens maintenance, recognizing microbial attack is crucial for ensuring the integrity of the lens, as it can affect performance and require specific cleaning protocols to eradicate the growth and restore optical clarity.