I would say discussion, which is one of the ones that Dr Safder Husain also mentioned. By contrast, I find describing methodology not so hard because I have a clear idea of what I did and I have a clear rationale for why I did it in that way.
I think results and discussion are the most difficult part of the research while methodology is the easiest part to write because the researcher must know what and how to do.
In my experience, the Methodology and Discussion sections of a research paper are the most challenging to write.
The Methodology section requires precise and detailed descriptions of the study design, procedures, materials, and data analysis methods. It's crucial to provide enough detail to allow replication without becoming excessively verbose.
The Discussion section involves interpreting the results, explaining their significance, comparing them with previous studies, and addressing the study's limitations. This section requires critical thinking and a balanced presentation of your findings.
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