India has a long tradition of religious pluralism, and peaceful co-existence of inter-religious faiths. What is this inter-mixing called?

syncretism

The correct answer is Option (4) → syncretism

Syncretism : A cultural phenomenon characterised by the inter-mingling or mixing of different religions or traditions. A hybrid of two distinct religious or cultural traditions.

The definition of Syncretism  is also given in  Glossary part of NCERT.