"You are going to drop the plate!"
Translation:Du kommer att tappa tallriken!
The suggested translation is with du, so you should probably interpret this sentence as spoken to one person, who is at risk of dropping his/her plate. It could easily be translated into English as You are going to drop your plate, see this discussion about why we prefer to use the definite in Swedish. https://www.duolingo.com/comment/6014446
If you're talking to several people who have one plate each, we'd say Ni kommer att tappa tallrikarna
What it suggests to you depends on what you input, it tries to give the closest possible match. It's possible to use ni to one person too, some people consider it polite, others hate it. Read more about that here: https://www.duolingo.com/comment/5591933 (read the comments too to get a picture of how differently native speakers look at this)
Skipping att in kommer att is increasingly common in Swedish. It's more or less acceptable these days. I still wouldn't really recommend using it in formal contexts, but it's becoming more and more common all the time. The course always has kommer att in the main translations but just kommer is supposed to be an accepted answer everywhere, too, and any accepted answer can get shown to you depending on what you input.