What is the tenure (Term) of office of the Members of Rajya Sabha?

Who is the ex-officio Chairman of the Rajya Sabha? Who presides over its meeting in the absence of the Chairman?

Mention any one exclusive power assigned to the Rajya Sabha by the Constitution.
Or
Mention any one power of the Rajya Sabha highlighting its role in India's Federal Setup.
Or
Mention any one power of the Rajya Sabha which is in keeping with the Federal character of the Constitution.

Mention any one exclusive power assigned to the Lok Sabha by the Constitution.
Or
Mention any one matter which shows that Lok Sabha is more powerful than the Rajya Sabha.