The correct option is
C chair
Noun is the name of a person,animal,place,thing or feeling. Thus, Option B,chair is the correct answer as it is the name of a thing.
Option C,have,is a verb. hence it is incorrect.
Option A,seat, is a part of the idiomatic expression 'have a seat'. So, it's part of the phrasal verb. Hence, it is not considered as a noun. Thus, the option is incorrect.
Thus, Option B is correct.
Option D is incorrect as we find the required answer in option B.