Answer
(a) hydrobromic acid
(b) periodic acid
(c) $HSeO_3$
(d) $HCN$
Work Step by Step
(a) For an acid containing hydrogen bonded to a halogen, we take the first part of hydrogen, $hydro-$, combine it with the first part of the name of the halogen with the ending changed to $-ic$, and add the word $acid$ to the end.
For $HBr$, we name it hydrobromic acid.
(b) For acids containing oxoanions that have the ending $-ate$ such as periodate, we merely take the name of the oxoanion, change its ending to $-ic$, and adding the word $acid$ to the end.
For $HIO_4$, we name it periodic acid.
(c) Here, we have another oxoanion bonded to hydrogen. $SeO_3^-$ is called selenite. Hydrogen has an oxidation number of $1+$ and selenite has an oxidation number of $1-$; therefore, we need only one hydrogen for each selenite ion. Thus, selenous acid has the formula $HSeO_3$.
(d) This acid is a combination of hydrogen and cyanide ($CN^-$) in a one-to-one ratio. Therefore, hydrocyanic acid has the formula $HCN$.
