Answer : 4. "Reserve Bank of India"
Explanation :

Solutions: The Reserve Bank of India (RBI) launched a pilot program for the wholesale segment of its central bank digital currency (CBDC) in the interbank call money market. According to media reports, nine banks, including four public sector banks and five private sector banks, are participating in the e-Rupee call money pilot. This is the second use case of a wholesale CBDC being tested, the first being introduced in the government securities market in November last year.