periodic motion is a motion of body wich repeats itself in equal intervals of time , but a oscillatory motion is a periodic motion which is about a mean position . so all periodic motions could not be a oscillatory motion , but all oscillatory motions are periodic in nature.

Oscillatory motion is also called vibratory motion while periodic motion is a motion which is repeat itself after a specific interval. Periodic motion may be rotatory or vibratory.

if a motion repeats it self after equal intervals of time it is called a periodic motion, if u understand this definition u will know that a fan is undergoing the periodic motion as if of its blades in proper words the blades of an electric fan is a periodic motion

Both. Periodic motion refers to any motion that repeats itself periodically. The oscillatory motion exhibited by swinging of arms is one type of periodic motion. Orbital motion of a planet is another type of periodic motion. The motion of a spring is another type, etc.

In actual conditions, a pendulum's motion can be seen as periodic, but decaying.