Yes, it is a form of the verb "to experiment." It is the past tense and past participle of the verb, but is not used as an adjective.
No, experimented is the past participle of the verb to experiment (experiments, experimenting, experimented).Example: The chef experimented with the recipe until he thought it was perfect.The word experiment is a noun; a singular, common, abstract noun.Example: The experiment paid off, it became a very popular menu selection.If you read the question it's referring to the word EXPERIMENTED, which is a VERB as per my first explanation about a describing word. A noun is the name of something.
Experimented is a past tense verb, not an adjective. The adjective would be experimental.
Beagles are the dog most experimented on.
mendel experimented with to learn about genetics
A lot of people have experimented with electrolysis, me being one of them.
He experimented with pea plants.
He experimented with hundreds of pea plants to understand the process of heredity.
Mendel experimented with pea plants to learn about genetics.
Joseph Priestley experimented to show that plants make oxygen.
Lawrence Hargreave experimented with box kites, laying the groundwork for pwered flight.
experimenting (the previous answer) is present tense of the verb... experiment is also a verb, and a noun, and some other things.. experimental is an adjective... but not sure its the one you want.
The word for a person being experimented on is a "subject."