The correct answer is option 'C', the President of India.

Explanation:
The power to declare castes or tribes as Scheduled Castes (SC) or Scheduled Tribes (ST) is vested with the President of India. Let's understand this in detail:

1. Constitutional Provisions:
The Constitution of India provides for the special protection and privileges of Scheduled Castes and Scheduled Tribes. The provisions related to SCs and STs are mentioned under Articles 341 and 342 respectively.

2. Article 341 - Scheduled Castes:
Article 341 empowers the President to specify the castes, races, or tribes or parts thereof as Scheduled Castes. This means that the President has the authority to declare any caste or community as a Scheduled Caste. Once a caste or community is declared as a Scheduled Caste, it becomes eligible for various special provisions and benefits provided by the government.

3. Article 342 - Scheduled Tribes:
Similarly, Article 342 empowers the President to specify the tribes or tribal communities or parts thereof as Scheduled Tribes. The President has the power to declare any tribe or tribal community as a Scheduled Tribe. Once a tribe or tribal community is declared as a Scheduled Tribe, it becomes eligible for various special provisions and benefits provided by the government.

4. Role of the President:
The President is the head of the state and exercises executive powers. In the context of declaring castes or tribes as Scheduled Castes or Scheduled Tribes, the President acts on the advice of the Parliament. The Parliament recommends the inclusion or exclusion of any caste or tribe from the list of Scheduled Castes or Scheduled Tribes, and the President gives assent to such recommendations.

5. Importance of Scheduled Castes and Scheduled Tribes:
The Scheduled Castes and Scheduled Tribes are historically marginalized communities facing social, economic, and educational disadvantages. The special provisions and benefits provided to them aim to uplift their socio-economic status and ensure their equal participation in the development process.

In conclusion, the constitutional authority vested with the power of declaring castes or tribes as Scheduled Castes or Scheduled Tribes is the President of India. The President acts on the advice of the Parliament in this regard.