The mega initial public issue of Anil Dhirubhai Ambani group's Reliance Power became the largest ever in India after over-subscription of more than 10.5 times on its opening day on Tuesday. Offered at a price band of Rs.405-450 for 228 million shares at a face value of Rs 10 each, the issue invited bids for 2,397,558,825 shares, data available with the Bombay Stock Exchange (BSE) and the National Stock Exchange (NSE) showed.