The correct answer is option 1: one-third of its members retire every two years. Rajya Sabha, which is the upper house of the Indian Parliament, is a permanent house in the sense that it is a continuous body that does not get dissolved, unlike the Lok Sabha. However, the members of the Rajya Sabha have a fixed term. According to Article 83 of the Constitution of India, the Rajya Sabha members have a term of six years. But, to ensure continuity, one-third of the members retire every two years, which means that there is a constant rotation of members in the Rajya Sabha. This allows for a balance between continuity and fresh representation in the house.