Interrogative adverbs are called adverbs because they ask for an adverbe / adverbial adjunct and something that stands for an adverbe / adverbial adjunct is an adverbe itself.
The accident happens at 15 o' clock. When happened the accident?
The accident happens at the crossroads. Where happens the accident?
He went to the refrigerator because he was hungry. Why he went to the refrigerator?
He has written the letter with a ball pen. With what he has written the letter?
He went to town dressed only with a bathing suit. How he went to town?
It is quite obvious that there are much more interrogative adverbs than interrogative pronouns because there are much more different types of adverbial adjuncts than different types of objects and each adverbial adjunct has its specific interrogative adverb.
perchè = why
Perchè non sei venuto alla mia festa?
Why you didn' t come to the party?
Perchè non mi hai detto niente?
Why you didn' t tell me about it?
come = how
Come è possibile che non abbia mai sentito parlare di questo?
How it is possible that you never heard about it?
Come funziona questo ?
How does it work?
In front of è, era and erano the final e is omitted, come becomes com'.
Com' è stato possibile che tu non sia arrivato puntuale?
How it is possible that you didn' t arrive in time?
Com' è possibile che non capisca qualcosa di così semplice?
How it is possible that he didn' t understand something so simple?
quando = when
Quando capirai che non si può sempre avere ciò che si vuole?
When are you going to understand that it is not possible to get always what you want?
When do you come?
Quandoshould not be confused with quanto, the last one means how many
Quanto tempo ci sei stato?
How much time have you been there?
Quanto ist ein waschechtes Adjektiv, wird flektiert, wir kommen darauf gleich zurück.
Quando ist ein waschechtes Adverb und wird nicht flektiert.
Da quando vivi a Parigi?
Since when do you live in Paris?
Fino a quando gli orrori continueranno a chiamarsi errori?
For how long the horror will be called an error?
Per quando devo finire questo lavoro?
Until when the work has to be done?
quanto = how many
Quanto is an interrogative adjective it matches so in number and gender with the noun it refers to
It is obvious that the singular forms ask for an amount of something, the plural forms for a number. It' s the same in English.
How much flour is needed to bake a cake?
How many euros the Goethe Intitute burns every year for junk culture while children die of trivial diseases?