Mumbai, Jan. 18 -- Ashok Chawla resigned on Friday, 11 January, as chairman of the National Stock Exchange of India Ltd (NSE) with immediate effect "in light of recent legal developments", the exchange said. The one-sentence press release gave no details. Chawla's resignation came on a day the Central Bureau of Investigation (CBI) told a special court in Delhi that it has obtained the sanction of the ministries concerned to file charges against him and four other former bureaucrats in the Aircel-Maxis case. Mint first reported on 5 November that Chawla would need to step down as soon as the CBI gets the go-ahead to prosecute him. Chawla had to step down as he was no longer "fit and proper" as per the regulations of the Securities and Exchan...