Question

What are the costs are coming under 2A

Answer 1

Below is a link to official Indian government websites that provide the list of SC/ST. 
[1] List of Scheduled Castes : Ministry of Social Justice and Empowerment
[2] Scheduled Tribes

Now, the question of number is difficult to answer - some castes span across multiple states - they are provided SC status in some state but not in others. Some appear in one or more states.

If you sum up statewise, you may end up counting them twice. If you count them by caste names only - you will have to de-duplicate them. Some caste names are spelled slightly differently in different states - that becomes a bit tedious and requires knowledge of the local language and their caste history etc.

You can take a rough estimate on the number of castes from these lists.

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