Preposition:

Sri Lanka is __ the south of India. And what will happen if Sri Lanka is replaced with any other state within the country India ?

Sri Lanka is____ the south of India

http://www.englishclub.com/grammar/prepositions-list.htm

Be sure to look up the meanings of any prepositions you're not clear on.
http://www.merriam-webster.com/

Below the south of India

The preposition that fits in the blank is "to". Sri Lanka is to the south of India.

If Sri Lanka is replaced with any other state within the country India, the preposition used will depend on the location of the state in relation to India. For example:

1. If the state is located to the north of India, you would use the preposition "to" or "in". For example, "Himachal Pradesh is to the north of India" or "Himachal Pradesh is in the north of India."

2. If the state is located to the east, west, or south of India, you would use the prepositions "to" or "in". For example, "Kerala is to the south of India" or "Kerala is in the south of India."

The specific preposition used will depend on the context and how you want to describe the location of the state in relation to India.

I want the answer of

Sri Lanka is __ the South of India .