The board of the country’s largest stock exchange NSE has given its nod to the CBI to prosecute two of its former MDs – Ravi Narain and Chitra Ramakrishna – relating to their role in misuse of the bourse’s trading mechanism. Last year, both Narain and Ramakrishna were arrested by the CBI for their role in a case for which an FIR was registered in 2018.