Is intonation used to ask a question in Vietnamese?
In Vietnamese, is there a word, syllable or sound used to show that a statement is a question?

In English, we show we are asking a question by raising our intonation.

In Japanese, they do this too, but there is also a question marker word, か.

Thank you.

Question

Is intonation used to ask a question in Vietnamese?
In Vietnamese, is there a word, syllable or sound used to show that a statement is a question?

In English, we show we are asking a question by raising our intonation.

In Japanese, they do this too, but there is also a question marker word, か.

Thank you.

Answer

Same like in English, we have 2 types of questions: Yes/No and Wh_ questions.

For Yes/No questions:

1. "không" at the end: negative answer -> Không; positive answer -> Có, (+ statement )

Is she beautiful?  - Cô ấy có đẹp không?
             Yes, she is very beautiful. - Có, (cô ấy rất đẹp)
             No. - Không

2. "phải không"/"đúng không" at the end (similar to tag question in English): negative answer -> Không/Không phải/Không đúng; positive answer -> Phải/Phải rồi/Đúng/Đúng rồi/Đúng vậy (There are quite a lot of sub words which go after the main words in Vietnamese ^^)

You are American, aren't you? - Bạn là người Mĩ phải không?
           Yes, I am. - Đúng vậy. 
           No, I am not. - Không.

3. "chưa" at the end (similar to Perfect Tense): negative answer -> Chưa; positive answer -> Rồi

Have you ever been to Vietnam? - Anh đã bao giờ đến Việt Nam chưa?
         No, I haven't. - Chưa, (tôi chưa đến Việt Nam).
         Yes, I have been there for 3 times. - Rồi, tôi đến đó 3 lần rồi.

4. "à" at the end (we use this in question to ask somebody to confirm something): negative answer -> Không/Chưa ; positive answer -> Ừ/Vâng (if the answerer is younger than the questioner)

He left already? - Anh ta đi rồi à?
          No, he's still here. - Chưa, anh ta vẫn ở đây.
          Yes, he left one hour ago. - Ừ, anh ta đi cách đây một tiếng.

Trang is cooking? - Trang đang nấu cơm à?
          No, she is watching TV. - Không, cô ấy đang xem ti vi.
          Yes, she is. - Ừ, (cô ấy đang nấu cơm)

For Wh_ questions:

Who/whom: ai
What: cái gì, con gì, công việc gì, ăn gì, uống gì, mặc gì, etc,.
When: khi nào, lúc nào, bao giờ
Where: ở đâu, ở chỗ nào, ở nơi nào
Which: nào -> which year - năm nào, which house - nhà nào, which film - phim nào, etc,.
How: thế nào, như thế nào

Did I miss something?

Answer

As in the Chinese language, you recognize a question by a "question particle" and not by its intonation. The question particle is not always located at the end.

For instance, a basic question in Vietnamese ends with the word "không" which means litteraly, "no".

Em ấy ở nhà không? --> She is at home, no?

To which you may answer by simply saying "không" if your answer is negative, she is not at home.  For a positive answer, you can repeat a part of the sentence, like "em ấy ở nhà".

Other interrogation particles take the place of where the answer would be located in the sentence. 
Example: Cái này là gì? --> Thing this is what?  Gì is the word for "what". 
Cái này là bàn --> Thing this is "a" table.

Ai tìm cô?: Who [is looking] you, madam? Who is looking for you, madam?
Cô tìm ai?: You [are looking] who, madam? Who are you looking for, madam?

Ai being for "who". Then, in your answer, you would simply replace "ai" by whoever it is.

I hope that helps!

Answer

Comment of Bianca is good. And I want to add some words:
1. " Chứ " :
Can I visit your house in the next time ? = Lần tới, tôi có thể đến thăm nhà bạn được chứ ?
2. " Hả " 
Did you eat ? = Ăn cơm rồi hả / à ?
3. " Sao " :
Why did you not answer my question ? = Sao anh không trả lời tôi ?