Tito Dioso Tubog It is absolutely fine to use a set of questions used in previous studies, as long as you specify it in your methodology the rationale for deploying that particular questionnaire protocol (e.g. to replicate the study...etc). Once you have referenced it properly, you are good to go as it adds more credibility to your study.

Thank you very much Shaitan Alexandra. Yes, I will include all your recommendtaions.

Yes you may if your study is measuring similar. However, do cite and reference the authors.

Thank you Sachin

Yes you can adopt and adapt them based on your variables.

Yes, if it could address your research question(s).