Answer:
Option A, Space
Explanation:
It is observed that the humidity(presence of water droplets) in the atmosphere filter out the infrared and ultraviolet radiations from the electromagnetic spectrum. Thus, for having a clear view of ultraviolet radiations it is better to place the telescope at a dry place (which is devoid of humidity).
Air at mountain's top is cold and dry and hence telescope at this location gives a better clarity. A telescope placed in a high-flying aircraft will give a clarity better than that of telescope placed at a mountain. Space is devoid of air and hence it shall give the best clarity of all the given options.
Thus, option A is correct
