The correct option is B Although
Let’s examine the sentence: “Even he worked hard, he failed in the examination.” The sentence brings out a comparison between two events of ‘working hard’ and ‘failing in the examination.’ The subordinate clause, “Even he worked hard” is supposed to add the element of surprise to the fact stated in the main clause, “he failed in the examination.” So, the conjunction that can serve this purpose better is ‘although.’ You use although to introduce a subordinate clause which contains a statement which makes the main clause of the sentence seem surprising or unexpected. So, ‘even’ should be replaced by ‘although’ in the sentence. Therefore, the improved sentence would be, “Although he worked hard, he failed in the examination.” Hence, Option B is the correct answer.