Explanation:

- Voluntary association: Trade unions are formed by individuals who voluntarily come together to pursue collective interests.

- Common goals: Members of a trade union work together towards shared objectives like better working conditions, higher wages, and job security.

- Intermediary: Trade unions often act as intermediaries between workers and employers to negotiate terms of employment.

- Individual actions: ? Trade unions focus on collective actions rather than individual actions, which are not characteristic of trade union activities.