Explanation
(C) panacea and (D) elixir are the credited responses.
The key words in this sentence are pretended, philosopher’s stone, and unmistakable. The context establishes a tone of exaggerated excitement surrounding the discovery in question.
Only (C) panacea and (D) elixir, both of which mean a cure-all, fit the needs here.
(A) paragon means a model of excellence or perfection; (B) a cataclysm is a sudden, violent charge; (E) palaver means flattery or empty talk.
(F) a triumph it may have been, but a more specific term is needed here