The Central Bureau of Investigation, CBI has questioned the Chief Executive Officer of Essar Group, Prashant Ruia as part of inquiries into the alleged allocation of 2G spectrum in 2008.According to the CBI officials, Ruia was questioned on day about his company's link with Loop Telecom Pvt. Ltd, which received 21 licences during the spectrum allocation. This follows questioning of Anil Ambani, chairman of Reliance Group by CBI.