Explanation:

Let’s break it down:

- Option 1: Employer

The employer obviously plays a big role in industrial relations, but they aren’t referred to as the ‘safety valve.’ Their main job is running the business, not mediating workplace stress or grievances.

- Option 2: Trade Union

Trade unions represent workers and negotiate on their behalf. They’re about collective bargaining and worker rights, but “safety valve” is not their nickname either.

- Option 3: Safety Officer

The safety officer handles things like machinery safety, fire drills, and accident prevention. Their focus is safety rules and regulations, not industrial relations per se.

- Option 4: Welfare Officer

This is it. Welfare officers are often called the ‘safety valve’ in industrial relations. They’re kind of like a pressure release—they listen to worker problems, mediate between staff and management, and smooth out issues before they blow up.