<prompt> Fatal dose of KCN is ?50 - 60 mg120 -130 mg180 -190 mg280 - 300 mg  <response>: Ans. is d i.e., 280 - 300 mg Fatal dose of hydrocyanic acid in the pure form is 50 - 60 mg while as sodium or potassium cyanide is 200 - 300 mg. 