When it's bad luck to meet a black cat?

Can you find out the number that should replace the question mark with a valid reason?

The person who makes it has no need for it. He who purchases it does not use it. The person who does use it does not know they are. What is it?

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?

There were three women in all the swimming costumes!
One was happy and the other two were sad!
The happy one was crying and the sad ones were smiling.
Why was this?

Who can jump higher than a Mountain?

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

Find The Next Number in the series:

12 13 15 17 111 113 117 119 123 ?

See the given image carefully. What you have to do is move the blue checkers in the position of the black checkers and vice versa. You are only allowed to move the checker to an adjacent empty space. Do it in the least possible moves.

John speaks the truth only once a day in a week. Below are a few hints for you:

First: Days are Sunday, Monday and so on.
Second: One day he says, "I lie on Monday and Tuesday".
Third: On the next day, he says, "Today is either Thursday, Saturday or Sunday".
Fourth: On the next day, he says, "I lie on Wednesday and Friday".

Can you identify the day on which he speaks the truth?