The AI-s version of the 50mm f/1.8 pancake lens from Nikon. This is the 2-series variant of the lens, with 2ft close focus distance and lightweight build.

Glass has minor dust inside and there is a small amount of fungus in the rear element as shown in the last photo (this photo was positioned and edited to bring out the fungus as much as possible - it appears much less than this in real life and doesn't affect photos taken with it).