Do hail stone fall down just when it is created? Density of ice is much higher than air. Then how can hail stone remain in earth atmosphere before they fall down ? 
 A: In the moist air of the clouds, the water condenses on dust particles. At the altitude where this happens, it is usually below the freezing point of water, so it quickly freezes. If winds and updrafts keep these particles of ice in the moist air, they collect more water. Eventually, the weight of the ice particles overcome the updrafts and fall to the surface.
Edit:
The updrafts are always present, due to the nature of the storm clouds.
https://en.wikipedia.org/wiki/Hail#Formation
https://www.classzone.com/books/earth_science/terc/content/visualizations/es1805/es1805page01.cfm?chapter_no=visualization
A: Hailstones - or anything like sleet, snow, etc - are formed by the freezing of water. Water droplets rise up, and as the temperature keeps decreasing, they freeze at a certain point into a stone, after which this stone would start falling. 
Certain studies say that the stone after falling, can enter an area with differenct conditions - causing it to maybe melt and start rising again. This keeps on happening and the stone keeps going up and down, until it doesn't encounter any more of the 'uplifting' conditions.
Whether hailstones are formed, or sleet or simply snow - depends on a lot of weather conditions.
A: Density is not an issue.  Winds can lift planes, cars, houses, and other things much heavier.
Hailstones can grow to 15 centimetres (6 in) and weigh more than 0.5 kilograms (1.1 lb).  It forms in strong thunderstorm clouds, particularly those with intense updrafts, high liquid water content, great vertical extent, large water droplets, and where a good portion of the cloud layer is below freezing 0 °C (32 °F).  Updrafts and winds can reach 110 mph (180 kph).
A: It's all density. Gravity should start to immediately pull it down.  The density of the cloud nor atmosphere can hold it up.  More than up draft would be needed
