Contrite means to be regret one's action. Obdurate means to refuse to change one's views. The 2 words are antonyms. Let us evaluate the options. Option A: Grievous means to do something bad and severe. Lamentable is a term used to denote that the action is bad or deplorable. The 2 words are synonymous. Option C: Sophisticated is a term used to describe a high degree of development. Cultured and sophisticated cannot be termed antonyms. Option D: Assenting means to give the nod. Favourable and assenting cannot be termed opposite in meaning. Option B: Aphoristic is a term used to describe that the claim is a general truth or widely accepted. Esoteric is a term used to denote something that is understood by a limited set of people. The 2 terms are opposite in meaning and hence, option B is the right answer