Prime Minister Narendra Modi said on Sunday that demonetization of 500 and 1,000 rupees notes was necessary to end corruption and black money and the step was taken to benefit the poor.In a speech after laying the foundation stone of the new Mopa Greenfield airport in Goa, Modi said: "The people have chosen a government and they expect so much from it. In 2014, so many people voted to free the nation from corruption."People have chosen our government to get rid of black money."Modi arrived in Goa earlier in the day to lay the foundation for two major infrastructure projects -- the Greenfield airport and an electronic city in north Goa.