Billionaire Mukesh Ambani's Reliance Industries on Monday showcased a truck that runs on hydrogen, the cleanest known fuel whose tail emissions are only water and oxygen, at the India Energy Week here. The Ashok Leyland manufactured truck with two large hydrogen cylinders was put up at a hall adjacent to the main venue where Prime Minister Narendra Modi inaugurated the three-day event that is themed around 'Growth, Collaboration, Transition.'