Pre-emptive scheduling is the most suitable scheduling scheme in a real-time operating system because it provides several advantages over other scheduling schemes in terms of responsiveness, prioritization, and meeting critical deadlines.

Responsiveness:
- In a real-time operating system, tasks or processes have strict deadlines to meet. Pre-emptive scheduling allows the operating system to interrupt lower priority tasks and switch to higher priority tasks immediately. This ensures that high-priority tasks are executed in a timely manner, improving overall system responsiveness.

Prioritization:
- Pre-emptive scheduling allows the operating system to assign different priorities to different tasks. This ensures that critical tasks are given higher priority and are executed before lower priority tasks. This is particularly important in real-time systems where certain tasks may require immediate attention and cannot be delayed.

Meeting critical deadlines:
- In a real-time operating system, it is crucial to meet critical deadlines for certain tasks. Pre-emptive scheduling ensures that high-priority tasks are given the necessary CPU time to complete their execution within their deadlines. If a low-priority task is currently running, the operating system can pre-empt it and allocate the CPU to a high-priority task to meet its deadline.

Context switching:
- Pre-emptive scheduling involves frequent context switching between different tasks. This allows the operating system to quickly switch between tasks and allocate CPU time based on their priorities. Context switching involves saving the current state of a task, including its registers and program counter, and restoring the state of the next task to be executed. This switching is efficiently handled by the operating system to ensure minimal overhead and maximum responsiveness.

Conclusion:
In a real-time operating system, where meeting critical deadlines and responsiveness are crucial, pre-emptive scheduling is the most suitable scheduling scheme. It provides the necessary prioritization and responsiveness to ensure that high-priority tasks are executed in a timely manner and critical deadlines are met. It allows the operating system to interrupt lower priority tasks and allocate CPU time to higher priority tasks, ensuring efficient and effective task scheduling.