Planning is an essential function of management that involves setting objectives, determining the best course of action, and allocating resources to achieve those objectives. It is a systematic process that helps organizations achieve their goals effectively and efficiently. There are several steps involved in the planning process, but one of them does not belong to this process. Let's examine each option to identify the step that does not fit in the planning process.

a) Making assumptions about the future:
Assumptions about the future are an integral part of the planning process. When setting objectives and developing strategies, managers need to make assumptions about future market conditions, customer behavior, and other relevant factors. These assumptions provide a basis for making informed decisions and planning for various scenarios.

b) Evaluating different proposals in light of the objectives to be achieved:
After setting objectives, managers must evaluate different proposals or options to determine which ones align with the desired outcomes. This step involves analyzing the advantages, disadvantages, costs, and potential risks of each proposal. By evaluating different options, managers can select the most suitable one that will help achieve the organization's objectives.

c) Allocation of jobs to members of each department:
This step does not belong to the planning process. The allocation of jobs to members of each department is part of the organizing function of management. Once the planning process is complete, and objectives and strategies are determined, the organizing function comes into play. It involves assigning tasks and responsibilities to employees, forming teams, and creating a structure that supports the achievement of objectives.

d) Seeing whether activities are performed as per schedule or not:
This step is part of the controlling function of management. After the planning and organizing stages, managers need to monitor and control the activities to ensure they are performed as planned. By comparing actual performance against planned schedules, managers can identify any deviations and take corrective actions if necessary.

Conclusion:
Based on the above analysis, it can be concluded that the step which does not belong to the planning process is the allocation of jobs to members of each department (option C). This step is part of the organizing function of management, whereas the planning process involves setting objectives, evaluating proposals, and making assumptions about the future.