Thiocyanic acid
Thiocyanic acid is a chemical compound with the formula HSCN which exists as a tautomer with isothiocyanic acid (HNCS). The iso- form tends to dominate with the material being about 95% isothiocyanic acid in the vapor phase.
It is a weak acid, bordering on strong, with a pKa of 1.1 at 20 °C and extrapolated to zero ionic strength.