Which one of the following is a periodic motion but not oscillatory ?
(i) Motion of pendulum of a wall clock.
(ii) Oscillation of a mass suspended from a spring.
(iii) Motion of a planet around the sun.
(iv) Vibrations of the wire of a guitar.

Explanation

To determine which of the given options represents periodic motion but is not oscillatory, we need to understand the definitions of periodic motion and oscillatory motion.

### Definitions:
1. **Periodic Motion**: This is motion that repeats itself after a fixed interval of time. For example, the motion of a pendulum or the revolution of a planet.

2. **Oscillatory Motion**: This is a specific type of periodic motion where the object moves back and forth about a mean position. Examples include the swinging of a pendulum or the vibration of a guitar string.

### Given Options:
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