Answer
(a) HCN - hydrochloric acid
(b) HNO$_3$ - nitric acid
(c) H$_3$PO$_4$ - phosphoric acid
Work Step by Step
(a) HCN - hydrochloric acid
Hydrogen (H), in an acid, has a valence of 1+. Cyanide (CN$^-$) has a valence of 1-. In this compound, we would need one hydrogen ion for every cyanide ion.
If the name of the anion ends in $-ide$, then we add the prefix $hydro-$ to the anion, change the anion ending from $-ide$ to $-ic$, and add the word $acid$ to the end.
(b) HNO$_3$ - nitric acid
Hydrogen (H), in an acid, has a valence of 1+. Nitrate (NO$_3$$^-$) has a valence of 1-. In this compound, we would need one hydrogen ion for every nitrate ion.
If the oxoanion ends in $-ate$, then we drop this ending, substitute the ending $-ic$ in its place, and add the word $acid$ to the end.
(c) H$_3$PO$_4$ - phosphoric acid
Hydrogen (H), in an acid, has a valence of 1+. Phosphate (PO$_4$$^{3-}$) has a valence of 3-. In this compound, we would need three hydrogen ions for every phosphate ion.
If the oxoanion ends in $-ate$, then we drop this ending, substitute the ending $-ic$ in its place, and add the word $acid$ to the end.
