This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Poisoning, Subject name: Anatomy
Yellowish discoloration of the mucus membrane and teeth is produced by 
Select and explain. 
A. Sulphuric acid, B. Nitric acid, C. Carbolic acid, D. Hydrochloric acid
B: Nitric acid
Answer: B: Nitric acid 
Explanation: Nitric acid- signs and symptoms They are similar to that of sulphuric acid. The abdominal pain and belching may be more. There may be severe cough, dysnoea, and breathlessness due to inhalation of fumes and irritation of air passages. There will be corrosion and yellow discoloration of the mucus membrane and teeth. Ref: FORENSIC MEDICINE AND TOXICOLOGY Dr PC IGNATIUS THIRD EDITION PAGE 409