What does A485 mean? And what does the values on the y-axis expresses? This question is from past exam paper. I don't want an answer to the multiple choice question below, I just want to understand what A485 means in the context of the question.
$A_{485}$ means the same thing as the text of the multiple choice question "absorbance of the solution at 485 nm". 

"nm" is an abbreviation for nanometers.

In other words, the absorbance of light having a wavelength of 485 nanometers is plotted on the y-axis of the graphs.