Thank you very much @Dr Atul G- LNG  and @Ehab Pilloor for your response. I really appreciate it.

The Percent Complete is calculated based on the number of certified business applications relative to the assigned task. For example, you have 1 certification task but having 4 applications to certify. If you completed 3, the Percent Complete will be 75%. This also means, that even the task may be in Closed Complete state but you did not certify the "application", percent complete is still 0.