The Broadcast View of Q&A is designed to be shared with the audience on a big shared screen. It includes the URL for attendees so everyone can see where they should submit their questions.
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You can find the broadcast view for Q&A in top toolbar of Q&A in Presenter View.

The Q&A Feed View shows a list of the submitted questions in upvoted order.

If you want to highlight a good question, or center the conversation around one, you can broadcast one question at a time. To do so, click “Broadcast” within a question’s toolbar. If the “Broadcast” button doesn't appear in the toolbar, click on the “... More” button and select it from there.

Note: This will replace the Feed View to show only that question.

You can also switch the individual question displayed while you're in the Broadcast View. You can swipe left or right. Plus you can click-drag or use the arrow keys on your keyboard.
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In slideshow mode, the broadcast view will cycle through the approved questions, pausing for a few seconds on each.

In the lower right corner, you'll see an Enable Slideshow option. 

This option is disabled by default, but you can enable the slideshow by clicking the link in the lower-right corner.