Which Chart Tool button allows you to quickly toggle the legend on and off? Chart Styles button
Chart Filters button
Chart Elements button
Chart Font button

The answer to this question is given below in the explanation section.

Explanation:

The correct answer to this question is:

Chart Element button

When you will insert a chart in excel, after inserting a chart in excel, when you click on the chart, then at the top right corner a button "+" will appear. This is called the Chart Elements button. By using this button, you can quickly toggle the legend on and off. By using this button you can add, remove, or change chart elements such as gridlines, title, legend, and data label, etc.

While other options are not correct because:

Chart Style button is used to change the style and color of a chart. Chart Filter button is used to filter the name and series of the chart and display them. While the chart font button is used to change the font of the chart.

plot immersion i am not fully sure with it though