The Basic plan has a limit of 100 slides. You can view your current total slide count from the Billing section of your Profile.
Once you have 100 total slides in your account, you will no longer be able to add additional slides, duplicate or copy slides or presentations, or recover deleted slides. You will be prompted to upgrade to a paid plan if you attempt any action that would add additional slides.
If you delete slides or presentations or remove shared presentations to reduce your total slide count, you will be able to add new slides as long as you don’t exceed 100 total slides.
NOTE: When deleting presentations to recover slide count, you must empty your trash to permanently delete the presentations.