Dismissal of an employee is a sensitive issue in the field of labor law, and it's important to understand what constitutes a fair dismissal. Let's analyze the reasons provided in your question.

• This reason is generally considered unfair. Dismissing an employee solely because they are a member of a trade union violates labor rights and protections. Employees have the right to join and participate in trade unions without fear of retaliation.

• This reason can be considered fair. Redundancy occurs when an employer needs to reduce their workforce, often due to economic reasons, restructuring, or changes in business needs. However, the employer must follow proper procedures, such as consulting with employees and considering alternatives to dismissal.

• This reason is also considered unfair. Dismissing an employee because of pregnancy is a violation of anti-discrimination laws. Employees are protected from being dismissed due to pregnancy or maternity leave, and such actions can lead to legal consequences for the employer.

In summary, the only reason among the ones listed that could be considered fair for dismissal is redundancy. Membership in a trade union and pregnancy are both protected characteristics, and dismissals based on these grounds are typically deemed unfair and unlawful.