$19\mathrm{.}62$ Naltrexone is used to help recovering narcotic addicts stay drug free.

$($a$)$ Label and name all the functional groups. Where relevant, indicate whether the group is

primary, secondary or tertiary.

$($b$)$ Upon addition of dilute hydrochloric acid solution, naltrexone forms a water$-$soluble salt.

Draw the structure of this salt.