This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Physiology
Smell of bitter almonds is seen in poisoning with 
Select and explain. 
A. Phosphorus, B. Hydrocyanic acid, C. Nitric acid, D. Oxalic acid
B: Hydrocyanic acid
Answer: B: Hydrocyanic acid 
Explanation: Cyanide can be a colorless gas, such as hydrogen cyanide (HCN) or cyanogen chloride (CNCl), or a crystal form such as sodium cyanide (NaCN) or potassiumcyanide (KCN). Cyanide sometimes is described as having a "bitter almond" smell, but it does not always give off an odor, and not everyone can detect this odor. Ref ganong's review of medical physiology 25e p143