What is a fundamental requirement for noncontributory plans regarding member participation?

In the context of noncontributory plans, a fundamental requirement is that 100% of eligible members must participate in the plan. This type of plan is designed such that the employer covers the entire premium, leaving no financial contribution required from the employees. As a result, participation is mandatory for all eligible employees; if they are part of the employee group, they must take part in the plan. This ensures that the employer can provide benefits uniformly across the employee base, enhancing the overall effectiveness and cost-efficiency of the insurance program.

The other options reflect various levels of participation that could apply to contributory plans or different participation requirements, but they do not align with the essential nature of noncontributory plans, which require complete participation by all eligible employees to maximize the benefits provided.