"He usually skips breakfast."

The correct answer is Option (2) → Adverb of Frequency

An adverb is a word that tells how, when, where or how much something happens. It can also describe an adjective or another adverb, for example she sings sweetly, very hot.

In this sentence, usually is the adverb. It means on most days, or most of the time. He skips breakfast on most days.

Option	What it tells	Example
(1) Adverb of Reason	why something happens	She was tired and hence went to bed early.
(2) Adverb of Frequency (answer)	answers how often?	Papa usually reads the newspaper with his tea.
(3) Adverb of Place	where something happens	Come inside, it is cold.
(4) Adverb of Manner	how an action is done: “usually” tells how often, not the way he skips it	Raju finished his work quickly.