Explanation:

Hail stones are a frozen form of precipitation that occurs when thunderstorm updrafts lift rain above the freezing level in the atmosphere. When hail stones become too heavy to be lifted by the updraft, they fall to the ground. x While most thunderstorms form hail, hail does not always make it all the way to the ground as hail. If the hail stone is small enough, the stone melts in the warmest portions of the atmosphere which are near the ground. For hail to become large enough to reach the surface, the stone must grow large enough in the thunderstorm before falling through the warm lower atmosphere. x Hail forms when a thunderstorm updraft lifts a water droplet above the freezing level in the atmosphere. The frozen water droplet then accretes super-cooled water or water vapor, which freezes once it comes in contact with the frozen droplet. This process causes a hailstone to grow. o Supercooled water is something unique–it’s water that is below its normal freezing point of 0°C (32°F) and yet remains a liquid. x Hail is often confused with other types of freezing precipitation such as sleet. Sleet is found mainly during the cold season and does not occur in thunderstorms. Hail, in comparison, is only found in thunderstorms where updrafts in the thunderstorm forces raindrops further up in the atmosphere to freeze. x In many cases, hailstones have a ringed appearance. The rings represent the different environments the hailstone experiences while moving through the updraft. When the hailstone is in an environment where mainly water vapor is present, a white or opaque layer forms. This occurs because small air pockets are trapped between the vapor particles as they freeze. When the hailstone is in an environment of mainly super-cooled water, a clear layer forms as the super-cooled water freezes instantaneously to the hailstone. x Hailstones can also grow by sticking to each other in a process called wet growth. Larger hailstones will ascend through the updraft at a slower speed than smaller hailstones. If the outer coating of these hailstones is not completely frozen, they can collide with each other and stick. If this process happens over and over again, a hailstone can grow very quickly. When these aggregated hailstones hit the ground, they often have a bumpy or spiky appearance (right), as the smaller hailstones that make up the larger hailstone maintain their individual shapes. x Hail sizes can differ greatly from one storm to another depending on the strength of the storm’s updraft. Stronger updrafts can create larger hailstones, which in turn causes more damage. x Favourable Conditions For Hail Formation: o Strong, upward motion of air (strong updraft) within the parent thunderstorm o High liquid water content o Great vertical extent of the cumulonimbus cloud o Good portion of the cloud layer is below freezing (o C or below) o High surface temperatures (hail growth is greatly inhibited during cold surface temperatures) o Hence option (d) is the correct answer.