このイスはあいていますか。

this (something or someone close to the speaker (including the speaker), or ideas expressed by the speaker)

chair; stool; post; office; position

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

to open (e.g. doors); to open (e.g. business, etc.); to be empty; to be vacant; to be available; to be free; to be open (e.g. neckline, etc.); to have been opened (of one's eyes, mouth, etc.); to come to an end; to open (one's eyes, mouth, etc.); to have a hole; to form a gap; to have an interval (between events)

indicates a question (sometimes rhetorical); or; whether or not; some- (e.g. something, someone); indicates doubt, uncertainty, etc.; emphatic prefix; suffix forming adjectives or adverbs; in that way