Which of the following Articles of the Indian Constitution mentions that the Vice-President of India shall be the ex officio Chairman of the Council of States?

The correct answer is Article 89.

Let us break down the relevant articles of the Indian Constitution to understand their provisions:
1. Article 89: This article explicitly states that the Vice-President of India shall be the ex officio Chairman of the Council of States (Rajya Sabha). It also details the election of the Deputy Chairman of the Council of States.
2. Article 90: Deals with the vacation, resignation of, and removal from, the office of the Deputy Chairman of the Council of States.
3. Article 91: Concerns the power of the Deputy Chairman or other person to perform the duties of the office of, or to act as, Chairman.
4. Article 92: Specifies that the Chairman or the Deputy Chairman is not to preside while a resolution for their removal from office is under consideration.

Therefore, Article 89 is the specific article that designates the Vice-President as the ex officio Chairman of the Council of States.