It's chipped, not acid eaten. You've hit the edge of the ram with something and it's chipped that finger, same as if it was the paint on the edge of a car door. But thats a considerably large chip to have flaked off, so could possibly be a manufacture defect if the finger naturally seperated from the pcb just by socket insertion.
If you look closely at those fingers, you'll see a darker line in the center. That's where it's actually making contact with the socket pins. That 1 finger is up beyond the contact area, so totally useless.
No idea if that's a power, ground, input or output data key or if that'd fully or realistically affect the ram overall. You'd have to memtest the ram stick individually, with comparisons against another stick.
If it were me, I'd chalk it up to a bad day and replace the ram, an expensive lesson, but a lesson nonetheless.
It's Gskill, rma is a possibility, so you could try that route, but as with any physical damage condition, the outcome is never a guarantee success.