Both the adverb strongly and the noun strongness are forms of the adjective strong.

The adverb is invisibly. Many -LE adjectives can form the adverb by changng the final E to Y (able, ably / simple,simply).

To change "sizzle" into an adverb, you can use "sizzlingly." For example, "The bacon sizzled sizzlingly in the pan."

Quickly is an adverb that could be used with moved, i.e. "The boy moved quickly through the crowd."

Purely is the adverb form of purity.

An example sentence for you is:
It is purely speculation at this stage.

Brightly is an adverb that pairs well with shine, as in "The sun shone brightly in the sky."

It can be, but only as the superlative form of "heavy" used as an adverb.

Heavy, heavier, and heaviest are all normally adjectives. But in some rare uses, both heavy and its comparatives can be used as adverbs.

e.g.

The snow is falling heavier than before. (more heavily)

Time hangs heaviest on their shoulders. (most heavily)

Yes, "furiously" is an adverb. It is used to describe how an action is done or the intensity with which something is done.

As an adverb, "creep" means to move slowly and stealthily, typically in a cautious or furtive manner.

No, "because of" is not an adverb. It is a prepositional phrase that typically functions as an adverbial phrase, providing information about the reason for an action or a cause.

Yes, "in the lab" is an adverb phrase because it describes where an action is taking place (in this case, "is").

There is not an adverb in the sentence "They opened a window because the room was too hot." You could easily add an adverb though, like so: "They quickly opened a window because the room was too hot."

The adverb form of "shake" is "shakily."

No, stability is not an adverb. Stability is a noun that refers to the state of being stable or not likely to change. Adverbs are words that typically modify verbs, adjectives, or other adverbs.

No, "sparkling" is not an adverb. It is an adjective that describes something as shining, bright, or lively. Adverbs typically describe verbs, adjectives, or other adverbs.

The adverb for "energy" could be "energetically."

No, "spilled" is a verb in the past tense form. Adverbs typically end in -ly and modify verbs, adjectives, or other adverbs.

The adverb form of "pollution" is "polluting." This adverb describes an action related to causing pollution.

Yes, it is an adverb. It is the adverb form of the adjective firm, and means in a firm way, or in a determined manner.

E.g.

The lines were firmly attached to the boat.

The governor firmly refused to compromise.

"Energetically" would be the adverb because it states how, why, or in what manner something was done. The word "energetic" would be the adjective, and since "energy" is a thing--form of power, like electrical energy or kinetic energy--then it is a noun.

No, "smells" is not an adverb. "Smells" is a verb that describes the action of perceiving odors. Adverbs typically modify verbs, adjectives, or other adverbs to provide information about how, when, or where something happens.

"Dizzy" can be both an adjective (describing a feeling of lightheadedness or confusion) and a verb (meaning to make someone feel unsteady or lightheaded). It is not commonly used as an adverb in English.

"Clothes" is not an adverb. It is a noun that refers to items worn to cover the body. Adverbs typically modify verbs, adjectives, or other adverbs to provide more information about how an action is performed.

Yes, in the sentence "Pull the rope hard," the word "hard" is used as an adverb. It describes how the action of pulling should be done.

No, "sudden" is an adjective. Adjectives describe nouns or pronouns, while adverbs modify verbs, adjectives, or other adverbs.