ANSWER: Chhandogya and Brihadaranyaka
Explanation:
The Chhandogya Upanishad mentions such subjects as the study of Vedas, Mathematics,
Mineralogy, Logic, Ethics, Military Science, Astronomy, Science dealing with poisons, Fine Arts and Crafts, Music, and Medical Sciences. The oldest among these are the Brihadaranyaka and Chhandogya which contain bold speculations about the eternal problems of human thought concerning God, man and the universe etc. King Janak of Videha organized conference of the learned, which is mentioned in the Brihadaranyaka Upanishad. The participants in this conference were Yajnavaikya, Uddalaka Aruni, Sakalya, Gargi and a number of other scholars. The details of this conference and various topics discussed there are given in Brihadaranyaka Upanishad. Only 11 Upanishad’s are important - Isa, Katha, Kena, Prasna, Mundaka, Mandukya, Taittiriya, Aitareya, Chhandogya, Brihadaranyaka and Svetasvatara. Sometimes a twelfth one is also considered important - Maitraya.
