Option A: Incorrect — Rajya Sabha is a permanent House. It is not subject to dissolution, unlike the Lok Sabha.
Option B: Incorrect — The term for elected members is 6 years, not 4.
Option C: Incorrect — One-third of members retire every 2 years, not 3.
Option D: Correct — If a seat becomes vacant mid-term, the person elected in the by-election serves only the remainder of the original term.