in operation vs operative

in operation is not a noun while operative is a noun.

Word	Noun	Adjective	Verb	Adverb
in operation	No	Yes	No	No
operative	Yes	Yes	No	No

in operation (noun)	operative (noun)
	someone who can be employed as a detective to collect information and assist in criminal investigations
	a person secretly employed in espionage for a government

in operation (adjective)	operative (adjective)
being in effect or operation	being in force or having or exerting force
	relating to or requiring or amenable to treatment by surgery especially as opposed to medicine
	(of e.g. a machine) performing or capable of performing
	effective; producing a desired effect