The word "in" is a preposition, but can be an adverb when used without an object (i.e not saying in or into what). In some cases it is synonymous with "inward."
Examples are:
The walls fell in.
The wolf pack closed in.
You have to bend the corners in.
The chairman was voted in by the council.
Adverb
"Use" can function as both a noun and a verb, but it is not an adjective or an adverb. When describing how something is utilized, you might use the adverb "used" in phrases like "used frequently." However, "use" itself does not serve as an adjective or adverb.
Yes, thankfully we can use it as an adverb. It is the adverb form of the adjective thankful.
You would have to use one of the adverb forms "thoughtfully" or "thoughtlessly."
(You would have to use the adverb, which is tenderly.) She touched his face tenderly.
Formulaically is the adverb form of formula.
As an adverb .
no
Like this: I did my history homework yesterday. That's how you use yesterday as an adverb in a sentence
In the English language, "fire" has no adverb form.
Adverb: I had a hat on. Preposition: I didn't have any money on me.
The adverb would be "inalienably." But it would have very limited use.