The correct option is A ignorant
The word 'omniscient' refers to knowing everything.
Option A, ignorant refers to lacking knowledge or awareness in general.
Option B, uneducated refers to having a poor level of education.
Option C, unqualified refers to not being sufficiently knowledgeable to do something.
Option D, backward refers to having made less progress than is normal.
Thus, according to the meaning, the word 'ignorant' is the opposite of the word 'omniscient'.