Some verbs require that they are expressed with a preposition to convey a certain meaning; for example think sometimes takes 'of' to mean 'about' or 'to know' (usually only:
I can't think of any good restaurants around here.
So, a question could be formed using this construction so as to end the sentence with 'of'
How many European countries can you think of?
In the 18th, 19th and to some extent the 20th, centuries, many grammarians prescribed that a sentence couldn't, or shouldn't, be ended with a preposition (as in Romance languages, like Latin, Italian, Portuguese etc.), so:
Who are you talking to? = To whom are you talking?
However, English is originally a Germanic language (like German, Swedish, Danish etc.) which allow sentences to be ended with a preposition (in fact in German it is positively necessary), so it would not be practical to deny this in English, given its linguistic history.
No, it is not a correct sentence. Consider rephrasing to "We will need your money the the end of March."
no
With the exception of capitalizing the first letter of the sentence and a period at the end, the sentence is correct.
Yes, "by the end of today" is a correct way to refer to something that will happen or be completed before the current day ends.
No, that wouldn't be a complete sentence. You could end a phrase with are. eg You are stupid. No I am not. You are!
"It is dark in the night." is a correct sentence if you remember to capitalize the first letter of the sentence and put a period at the end.
Yes, "n'est-ce pas" is a French expression that translates to "isn't it so" in English. It is commonly used at the end of a sentence to seek agreement or confirmation, but it is not as commonly used in English as it is in French.
No, "When does the sale end" is better.
It may be. There is no word in English that cannot begin or end a sentence. The idea that certain word are unfit to end a sentence comes from Latin grammar, not English.
Yes, it is grammatically correct to end a sentence with the word "so." However, it may be informal or conversational in style.
Yes, it is grammatically correct to begin a sentence with a preposition in certain cases, especially in informal or conversational writing. However, it is generally avoided in formal or academic writing.
If my computation is correct, the world will end this December.