Nitrogen's freezing point is -210 degrees Celsius, or 61 Kelvin. This temperature is hard to reach because of the difficulty in pulling heat from the environment to allow the temperature to drop. After nitrogen freezes, it exists in a form that looks like snow.
Although purely liquid nitrogen is thought of as a coolant, it actually is less effective than a slush of partially frozen nitrogen. This is because liquid nitrogen in contact with a warmer object almost instantly boils and creates an insulation of gas, making it more difficult to lower an object's temperature. The slush does not transfer heat as quickly.