Yes

And actually some textbooks tell you that since "か" can indicate a question, you don't need the question mark "?" after the sentence. I may tell you that this is true for formal contexts, but due to the influence of Western languages, question marks are quite common in daily life, so don't be surprise if you find question marks in anime or manga.

I've seen words like わたし become わたしたち to create plurals, but I'm no expert.

You can add たちto indicate groups of people ie 僕たち

I thought there was. Things like あなた becoming あなちち?

Somewhat interesting side note: -たち is a suffix that adds to any noun referring to a person to "pluralize" it, e.g. 彼女たち = "the girls", イギリス人たち = "the (specific group of) British people", 田中たち = "the group of people with Tanaka", and even 学生たち = "the students".

Even more interestingly, as far as I understand 「学生たちですか」removes all ambiguity about the subject, even though it is omitted, and can only translate to "Are they students?" That is to say, you can't collectively ask a group of people "Are you students?" using 「学生たちですか」

Isn't かのじょ used for girlfriend as well? The kanji writing is different from 彼女?

Plural is implied in Japanese, for the most part. It can mean either ,,Are you a student?'' or ,,Are you students?'' Either one is technically correct, given that there is no more context.

It corrected you to the closest thing to what you'd said... "are you students" and "are you a student" are both right, but "are you student" is incorrect grammar in English and so it counted as incorrect

It means both "are you a student?" and "are you students?", it can even mean "is he a student?". This is because the pronoun is implied by the context, as is the difference between singular and plural. In English, there are also some instances where the difference between singular and plural is implied by the context, as in "Are you happy?": when asked to one person, the sentence is singular; when asked to several people at the same time, the sentence is plural.

Yes, it can, in a different situation. It doesn't simultaneously meaning "are you a student" and "am I a student" though.

There is no subject, so it is determined purely by context. In this case we assume you're talking to someone, so the default subject becomes "you" (the other person)

Sei has to do with the second kanji 生 which means "life" amongst other things. If you check a Japanese dictionary (say, jisho.org) it reveals the individual meanings of each kanji for gakusei and sensei

Good try, but not quite. Your sentence would mean "Students too?"

Remember that the full sentence (of the exercise) is typically あなたは学生ですか？ where は marks out that you are asking "you = student?" In order to maintain the same grammatical structure, you need to replace は with も, in other words あなたも学生ですか？ This time, も does は's job and adds the "also" emphasis to the word that came before it, "you also = student?"

Note that this requires you to explicitly make reference to the subject, but it isn't considered rude to use あなた (unless you know the person's name, in which case you are expected to say "name-さん" to be polite). This is because the use of も is to emphasize the subject, and it's understood that you can't do that while leaving out the thing you want to emphasize.

If you mean to specify "you" or "me", it's done by putting "Anata wa", or "Watashi wa", respectively, in the beginning. Example: "Watashi wa aoi desu (I am blue)"

学生 (がくせい) is the word for student(s)

The first 2 symbols (gaksei)

Almost all kanji have multiple readings, usually two or more different pronunciations. A general rule of thumb is that the on'yomi (Chinese-derived reading) is used when the kanji is used in combination with other kanji, and the kun'yomi (Sino-Japanese derived reading) is used when the character is on its own or combined with hiragana.

I think it's just Duo's TTS program not being set up correctly to identify which reading is appropriate in this context. It treats each of the kanji separately, hence it gives you the kun'yomi reading for 生 when we actually need the on'yomi.

To say "am I a student", point at yourself first and say 学生ですか？ (to really sell it like you're a native speaker, point to your nose instead of your chest ;)) But seriously, pointing at yourself provides enough context for the assumed subject to change to "I".

Another, potentially less natural, option would be to explicitly state the subject so that it doesn't need to be assumed: 私は学生ですか？

Yes, because the subject is provided by the context, as is the case in the vast majority of Japanese sentences.

It's not quite that simple. お is added to some words to indicate respect. Because Japanese people generally use respectful language when referring to others and humble language when referring to themselves, adding お often implies that the word refers to the other party (in most cases, "you").

Also, in theory, most words can take an honorific prefix (お- or ご-), but in practice, the large majority of words sound unnatural with honorific prefixes. There isn't any rhyme or reason for it that I know of; it's just a matter of what is/isn't commonly accepted.

I've already answered this question in an earlier comment:

Almost all kanji have multiple readings, usually two or more different pronunciations. A general rule of thumb is that the on'yomi (Chinese-derived reading) is used when the kanji is used in combination with other kanji, and the kun'yomi (Sino-Japanese derived reading) is used when the character is on its own or combined with hiragana.

I think it's just Duo's TTS program not being set up correctly to identify which reading is appropriate in this context. It treats each of the kanji separately, hence it gives you the kun'yomi reading for 生 (naMA) when we actually need the on'yomi (sei).

Duolingo wants you to use proper (or at least substantial) English so that it can teach you proper (or substantial) Japanese. "U" is both informal and (in many cases) seen as incorrect.

Sorry if I sound like a stick in the mud, but it's not going to kill you to type in two extra letters.

You didn't translate the full sentence. The full sentence is "Are you a student?"