No, it is not. It is the past tense and past participle of the verb to purchase. It can be a verb form, a participial, or an adjective (bought, paid for).
It can be a verb, a noun, or, informally, an adjective. You can bargain with someone, (verb), you can be given a bargain on a purchase (noun), or you can purchase a bargain item (adjective). The use of "bargain" as an adjective is not considered technically correct, but it is still occasionally used in informal contexts.
The verb to hire has the participle adjectives hiring and hired. For the noun hire, it can be used as a noun adjunct (hire car, hire purchase).
"Secondhand" is usually an adjective: He bought a secondhand car where secondhand describes the car as used or previously owned."Secondhand" can also be used as an adverb: He bought the car secondhand where secondhand describes the manner in which he made the purchase.
No, it is a verb or a noun (to go around, to surround; a round shape). The adjective form is circular.
It is an adjective.It is a an adjective.
No, it is not an adjective. Differently is an adverb.The adjective would be different.
No. It is not an adjective. An adjective describes something.
Cautious IS an adjective. An adjective is an action!
No, it is an adverb. The adjective is clumsy.
It can be. "Ideal" is an adjective and a noun.
It is not an adjective. It is a noun based on the adjective unfit.
Yes, it is an adjective.