Explanation:
The visible light coming from celestial bodies from space are affected most by the atmosphere. The visible light suffer blurring and absorption. So, to avoid such situation optical telescopes are kept in mountains where atmosphere is thin.
Whereas radio signal are not affected by the atmosphere so, they need not be placed in mountains.However, it is affected by various noises from the man made devices. So, to avoid these noises radio telescopes are kept in deep valleys.
