Which of the following examples represents periodic motion ?
(i) A swimmer completing onė (return) trip from one bank of a river to the other bank.
(ii) A freely suspended bar magnet displaced form its N-S direction and released.
(iii) Halley's comet
(iv) A hydrogen molecules rotating about its centre of mass.
(v) An arrow released from a bow.

Explanation

To determine which of the given examples represents periodic motion, we first need to understand what periodic motion is. Periodic motion is defined as motion that repeats itself at regular intervals of time. Let's analyze each option step by step.

**Step 1: Analyze the swimmer's motion.**
- A swimmer completing one return trip from one bank of a river to the other bank involves back and forth movement. However, the time taken for each trip can vary based on various factors (like current, swimmer's speed, etc.). Therefore, this motion does not repeat at regular intervals.

**Conclusion:** This is not periodic motion.

**Step 2: Analyze the freely suspended bar magnet.**
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