What tool in Mendix helps visualize the relationships between entities?

The tool in Mendix that helps visualize the relationships between entities is the Domain Model. The Domain Model is a critical component in Mendix that provides a graphical representation of your application's data structure. It allows developers to define entities, attributes, and their associations, effectively showcasing how different entities relate to one another within the application's data model.

By using the Domain Model, developers can easily see and manage relationships such as one-to-one, one-to-many, and many-to-many associations. This visual representation aids in understanding how data is organized and ensures that the relationships are set up correctly, which is essential for ensuring data integrity and optimizing application performance.

The other options, while useful in different contexts, do not serve the same specific purpose. The Project Explorer is focused on the overall project structure and navigating through the components of the application, but it does not provide a visual representation of entity relationships. The Model Viewer is designed to present the UI model but does not emphasize data relationships, and the Data Store relates to where data is persisted rather than how entities connect with each other conceptually.