What key question does experimental research aim to answer?

Experimental research primarily seeks to determine causal relationships between variables. The key question it addresses is whether variations in one variable can directly cause changes in another variable. This involves manipulating an independent variable and observing the resulting effect on a dependent variable, which helps establish cause-and-effect relationships.

In contrast, the other options pertain to different aspects of research. The observable characteristics of a sample are identified through descriptive statistics, which aim to summarize and describe data rather than establish causation. Measuring internal attributes involves assessment techniques but does not necessarily imply understanding their causal relationships. Lastly, determining the number of scores in a population relates to understanding the size of the population, which is critical for statistical analysis but does not engage with the primary aim of establishing causation that is central to experimental research.

Hence, the correct answer focuses on the core objective of experimental research design, which is foundational for exploring causal relationships in scientific inquiry.