You may include the definitions in Chapter One (both conceptual and operational). Don't forget the sources. Since you are from UPM, I'm sharing with you the guideline to thesis preparation. It's better to start early ;)
I would concentrate on conceptual issues in the introductory chapter, and then treat issues of measurement (operationalization) in the Methods chapter.
Conceptual definition can be explained in the introduction or in a separate section conceptual or theoretical framework and operational definition in the methodology section
Operational definitions are mainly concerned with how you measure the variable, therefore, I would suggest methodology section/ chapter is the appropriate place for Operational definitions
I will say that conceptualization should be explained in the introduction (chapter one). How to measure the variables, some of which you have conceptualized (operationalization), are rather suitable in the research methods section of the study.