I don't know What 'for which' is means and why it is used in this line He played a leading role in the Mariner, Viking and Voyager expeditions to the planets, for which he received the NASA medals for Exceptional Scientific Achievement and for Distinguished Public Service, and the international astronautics prize, the Prix Galabert. I'ts from Cosmos the book I though I was certain that I am quite familiar with 'which and that', that called relative pronoun. but sometimes a relative pronoun accompanied with preposition takes me nowhere like for which, by which, in which. Because I am intimately familiar with Korean so If anybody can explain in Korean then that must be more helpful than in other language but not that you should answer me in Korean.