Final answer:
The correct IUPAC name for HCN(aq) is hydrocyanic acid when it acts as an acid, particularly in aqueous solution.
Step-by-step explanation:
The correct IUPAC name for HCN(aq) is hydrocyanic acid. When naming as acids, a prefix of hydro- is added to the name of the anion, changing the ending from -ide to -ic acid. Therefore, since the anion is cyanide (CN-), the name hydrocyanic acid is used when this compound acts as an acid, especially in aqueous solution. This naming convention is similar to other acids such as hydrochloric acid (HCl), hydrobromic acid (HBr), and hydrosulfuric acid (H₂S).
However, when this compound is not acting as an acid, for example, when it is in the gaseous state, the name of the cation element, which is hydrogen, is followed by the name of the anion without the word 'ion' at the end, resulting in hydrogen cyanide as the name.