Coronic acid

From TARDIS Index File, the free Doctor Who reference.

Coronic acid is a type of acid that is harmful towards Sontarans, causing damage to both themselves and their armour. Chessene used it to kill two Sontarans. (DW: The Two Doctors)

Coronic acid was also used in 2370 by Raghi defence forces to defeat a Sontaran assault force. (MA: Lords of the Storm)