Answer: The right answer is "There was no deceiving himself: something terrible, new, and more important than anything before in his life, was taking place within him of which he alone was aware. Those about him did not understand or would not understand it, but thought everything in the world was going on as usual. That tormented Ivan Ilych more than anything."
Explanation: Just to elaborate a little on the answer, it can be added that the other three excerpts (from "At the law courts" to "for jests," from "Ivan Ilych settled down" to "he usually won," and from "Ivan Ilych was esteemed" to "more attractive") do not revolve specifically around the theme of loneliness. This is particularly true of the last two excerpts, which describe his pleasant life in the new town and his attractive duties as Assistant Public Prosecutor. The second excerpt does mention that people looked at him strangely, as if they knew that his life was about to end, and that his friends made jokes about his mood, but the first excerpt provides a stronger evidence of his loneliness. What really tormented him was the fact that only he was aware of his inner condition, and those around him, particularly his wife and daughter, ignored his anguish.