Hi Ashvini,
These are some really great questions. EEFs and OPAs appear throughout the PMBOK, and you will come into them almost every chapter. In order to make sense of EEFs and OPAs, one must first understand what they define and how they affect the project.
EEFs refer to conditions, not under the control of the project team, that influence, constrain or direct the project
OPAs are the plans, processes, policies, procedures, and knowledge bases specific to and used by the performing organization. These assets influence the management of the project.
Source: PMBOK 6, pg 38-39
When you are studying, it is best to understand what the specific EEF/OPA will do to the particular process, instead of memorizing which process has what as EEF/OPA
Hope this helps,
Joe