Step 1: Understanding the Term 'Ex-officio'
"Ex-officio" means "by virtue of one's office". An ex-officio position is a position someone automatically holds because of another office they hold. The question asks who is the ex-officio Chairman of the Rajya Sabha (the Council of States).
Step 2: Constitutional Provision
Article 64 of the Indian Constitution explicitly states: "The Vice-President shall be ex-officio Chairman of the Council of States and shall not hold any other office of profit." This is one of the primary functions of the Vice President of India.
Step 3: Evaluating the Options
(A) Deputy Speaker of Loksabha: Presides over the Lok Sabha in the Speaker's absence. No role in Rajya Sabha.
(B) Vice President: As per Article 64, the Vice President is the ex-officio Chairman of the Rajya Sabha.
(C) Senior Most Member of Rajyasabha: A senior member may act as a pro-tem Chairman to administer oaths, but is not the permanent Chairman. The Deputy Chairman is elected from among the members, but the Chairman is the Vice President.
(D) Senior Most Member of Loksabha: Has a similar pro-tem role in the Lok Sabha but no role in the Rajya Sabha.
Step 4: Final Answer
The Vice President of India acts as the ex-officio Chairman of the Rajya Sabha. Therefore, option (B) is the correct answer.