Can you find out the next digit in the following series ?

0, 0, 1, 3, 2, 6, 3, 9, 4, 12, 5, ?

When I go in I might cause pain. I cause you to spit and ask you not to swallow. I can fill your hole. What am I?

Which is the smallest number that you can write using all the vowels exactly once?

I have one of the three numbers: 1, 2, or 3 in my mind. I speak only truth. You can ask me just one question for which I will only reply in yes or no or don't know. What question will you ask from me so that you are able to know the number?

Solve the equation in the image by looking at the pattern closely.

How can you spell "White of an egg" in one word?
Hint: I know you can spell coke, poke, and joke.

One day, I thought of ways that can be used for creating a palindrome. So I decided that I will turn into a larger number by adding the reversed digits to the original number and keep doing it till I finally obtained a palindrome.

I am not sure if this process will always result in a palindrome eventually but I was able to produce a four-digit palindrome. Can you guess my starting number?

Why is a river so rich ?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C