False. Citations come in two parts: the full, detailed citation + the abbreviated in-text citation. (This gets a little different in Chicago Style footnotes, but we'll ignore that technicality for now.)
If you have a lovely and perfect list of all your sources... but haven't indicated where or how any of them were used anywhere in your project... well, that's not good. (Plagiarism.) You must use in-text citations (usually parenthetical, but also narrative) to indicate where ideas or phrasing came from originally. This gives credit to your sources more specifically and makes it clear what's original to you.
If you repeat any language verbatim, that content must be inside quote marks and you must provide the citations. If you paraphrase the information (often preferred!), take care that you're really synthesizing the information and not just swapping out synonyms.
See also: the Citations vs Plagiarism page of this guide.
False. Honestly, most cases are probably accidents to some extent -- careless slips or genuinely not knowing something would count as plagiarism.
As the saying goes, ignorance of the law is no excuse... but will your professor flunk you for accidentally missing a single in-text citation in one paper? Probably not. Keep your guard up, but there's no reason to be paranoid. Learn some best practices for prevention.
False. It's unethical and can wreck your reputation...but plagiarism itself is not against the law. You might fail your assignment or class or be expelled (or be fired or sued)...but there's no plagiarism police to fine you or jail you.
That said, you could plagiarize in such a way as to commit copyright infringement at the same time, and there are indeed laws against that. As you produce work outside a classroom (maybe a project gets published, or you're creating something for your job), this becomes more relevant.
Mixed. Presentations are very visually-oriented in a way papers are not, and none of the style guides (at least, neither MLA nor APA nor CMOS) make any requirements about slideshows -- there's no rules for margins or font sizes or whatever like there are for documents.
That said, you can still write your citations in a particular order, even if everything else about them looks different.
You should plan to include in-text (in-slide?) citations in your presentation, just like you would do with your essay, and these too should match the citation style you're using. You have more flexibility about placement. After all, you're not typically supposed to be placing full sentences on a slide, so the rule about tacking on citations at the end of the sentence doesn't really apply! Just make sure it's clear which source goes where if more than one is at play on a single slide.
False. When students bring this up, it seems like they're thinking in one of these ways:
1. "What if I have an idea that someone else already had? Won't I get busted for plagiarism?"
Not really. People arrive at the same ideas independently sometimes! (Fun fact: Charles Darwin almost wasn't the first to publish on the theory of evolution.) Being able to show your receipts by way of your sources establishes how you arrived at that idea yourself.
However, if you haven't done your citations... it will look as though you're passing off others' work as your own. Or maybe you do have citations but you copy/pasted a lot of material: there's not enough of you and your thoughts in the paper.
While it's feasible to have the same basic ideas others have had, the odds that you used the exact same sources, with the exact same selection of evidence, written in the same style are pretty astronomical.
2. "The experts already wrote about this. Why am I trying to improve or change anything that they wrote?"
While it's often true that undergraduate students aren't typically creating new knowledge for their field (that's what you do when you seek a PhD), you are still contributing your own take on a topic. At the very least, the whole point of any assignment is for you to demonstrate that you can think about the subject and express those thoughts clearly: you should be logical if not brilliantly original.
That said, it's incredibly unlikely that you'd by sheer coincidence lay out a similar argument using similar wording as someone else when you hadn't read their work. You and your classmates could all receive the exact same topic and the same selection of sources to use, and you should all be submitting unique papers despite that!