The following line is from an SAT excerpt where the author really(!) dislikes the way science was being taught (in 1939).Here's Michael Weiss:
(24) "As to the learning of scientific method, the whole thing is palpably a farce."
3. The word ‘palpably’ (line 24) most nearly means
The answer is B.
Markedly is wrong because, notwithstanding the fact that its dictionary definition is virtually identical to that of obviously, the two words are used in quite different ways. Markedly is only used in comparisons: Today is markedly warmer, my son is markedly taller than my daughter, this question is markedly harder than the other. You would never say: My son is markedly tall or Today is markedly warm. So markedly is not equivalent to palpably in the given sentence.
Not to put too fine a point on it: Of the two choices, "obviously" is markedly a better fit than "markedly," and so it is obviously the right choice. :)