What is the feminine of in Italian?

There is no feminine form of "in" in Italian. The word "in" is gender-neutral.

Here are some examples of how you might use "in" in Italian:

* Sono in casa. (I am at home.)

* Il libro è in biblioteca. (The book is in the library.)

* La chiave è in tasca. (The key is in my pocket.)

In all of these cases, "in" remains the same, regardless of whether the subject is masculine or feminine.