Explanation:

- Act: Refers to a specific deed or action, often with a focus on performance. A musician singing at a concert falls under this as it’s a single, focused activity.

- Action: A broader term than "act" and can refer to any kind of doing or activity. This applies but does not specifically focus on the performance aspect.

- Process: Involves a series of actions or steps taken to achieve an end. A concert includes processes, but the singing itself is more aligned with one act.

- Collective Behaviour: Refers to social processes and events which do not reflect existing social structure. This doesn't directly relate to an individual performing.

Answer: Option 1 - Act