Acid pellets are small projectiles formed of acid. The Autobot Prowl uses a gun that is capable of firing acid pellets, as well as lasers. Scattershot wields an atomic acid pellet gun, which is also used by Computron. A shot from Scattershot or Computron will burn you. And irradiate you.
Prowl uses acid pellets against the uncontrollable Autobot X (Autobot Spike) and to disarm a group of outlaws from out of the Old West that emerged from out of a temporal anomaly. (Dinobot Island, Part 2)