Answer to Question 1
An operational definition is one that defines a construct in terms of the operations that researchers must perform in order to measure the construct. They are important because they specify observable events that represent abstract constructs and thus make research on the construct possible.
Answer to Question 2
Mixed methods research combines both quantitative and qualitative approaches within a single study. It has the advantages of each approach and may result in findings that are more dependable and complete than either method alone could provide.
The structural formulas show the state of ionization that would predominate at pH 7.0
Percentage of Americans Living in Communities with a Fluoridated Water Supply, by State. 2012
Very nice definition of time
Importance of Considering Gestalt Principles in Product Design
The Definition of Intelligence