Answer: Scatter plot.

**Explanation:** - **Option A (Tree-map):** Incorrect. A tree-map is primarily used for displaying frequency distributions or hierarchical data, where the area of each rectangle represents the value of a group. It is not designed to illustrate correlations between variables. - **Option B (Scatter plot):** Correct. A scatter plot is an effective graphical tool for visualizing the relationship between two numerical variables. It plots individual data points on a two-dimensional plane, making it ideal for identifying trends, patterns, or correlations between the variables. - **Option C (Clustered bar chart):** Incorrect. A clustered bar chart is useful for comparing frequency distributions across categories, particularly for categorical data. However, it does not provide insights into the correlation between two variables.

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