This bar chart visualizes the average pollutant value for each country from a CSV dataset of world air quality. The chart uses D3.js v7 with an SVG rendering approach, employing `d3.scaleBand` for the categorical x-axis and `d3.scaleLinear` for the continuous y-axis. The data is aggregated using `d3.rollup` with `d3.mean` to compute country-level averages. Bars change color from steelblue to orange on mouseover, providing interactive feedback to the viewer.