1. ice cream- Words are usually separated by spaces, but every major American dictionary treats this as one word, and these give “noun” as its part of speech. Steven Pinker defines one of the senses of word as an entity that the rules of syntax cannot separate or rearrange. That seems to be the sense of ice cream that would make it one word.
2. crisp and crispy- When referring to something nonphysical use crisp: crisp morning; when referring to something physical, use crispy: crispy fries. You can use either, but it just doesn’t sound right.
3. Yes, it’s log in to or log on to, though most ppl use log into/onto.
4. pants- What Illuminattile said is correct. I would just add that those in the clothing trade consider a pair of pants to be a pant. It’s correct but only clothing people use it. I guess if you talk about pants day in and out sooner or later you’re going to say “Let me show you a different pant,” rather than pair of pants.
5. Is it correct to say "The purpose of this report is" and then list two or more items? How about "The purposes of this report are?"
It seems illogical to tell people that a report has one purpose and then declare that purpose to be a whole range of things. However, if the list to follow amounts to one complicated thing, I think purpose is fine. If the list really does cover a bunch of things, change purpose to goals or revise the sentence to read “This report is intended to serve four purposes” or something like that.
6. skies- yes, skies is a perfectly good word. “O beautiful for spacious skies, for amber waves of grain…”
7. God/god- Illuminattile covered this well.
8. dairy- In four of the seven major American dictionaries dairy is not defined as anything that can be consumed. But three do say that it can be used to mean “dairy products.” This variation suggests that dairy meaning “dairy products” hovers at the edge of contemporary mainstream English.
9. Daylight Saving/Savings Time- Both variations are acceptable; however, all major Amer. dictionaries agree that none of the words in the phrase should be capped. So: daylight saving time it is.
10. into and in to- The adverb in followed by the preposition to is not to be confused with the preposition into. Because if you say “The suspects turned themselves into the police,” it sounds like they’re magicians or aliens who can change their appearances…It should be in to.
Should "The United States is full of idiots" be "The United States are full of idiots"?
No, because most ppl are referring to one country, one entity, when they use the United States. If they are referring to the states individually then, yes, it would be followed by are.