The correct answer is A. ignorant.
An ignorant person is someone who lacks knowledge or awareness in general; uneducated is someone who has not received a formal education; unqualified is someone who does not have the necessary skills or experience for a particular job or task; and backward is someone who is old-fashioned or out of touch with modern ideas.
In the given question, the person is putting on airs and claiming himself to be omniscient. This means that he is pretending to know everything, even though he does not. This suggests that he is ignorant, as he does not have the knowledge that he claims to have.
The other options are incorrect because they do not accurately describe the person in the question. The person is not uneducated, as he may have received a formal education. He is not unqualified, as he may have the skills and experience necessary for a particular job or task. And he is not backward, as he may be up-to-date with modern ideas.