Closing participation for specific slides can be useful if you need to explain a question before your audience votes, or for any other reason where you do not wish the participants to respond to a question at that moment.

If you want to close responses completely for all slides, you can disable participation for the whole presentation instead.

You can close and open participation for a specific slide from the Presentation View, by clicking on the three dots in the Presentation menu at the bottom of the screen and selecting Turn off responding:

You can also use your keyboard shortcut by clicking "C" on your keyboard to quickly enable and disable participation.

To let your audience respond again, simply follow the same process: go back into the Presentation Menu and click Turn on responding, or use the shortcut "C" on your keyboard to toggle between enabling and disabling responses while presenting in fullscreen.