Complete the table series riddle by finding the number that can replace "??".

What has many keys but can’t open a single lock?

Can you make a six-letter word using the letters N, A and B ?

Do you know of a place where the wind blows south and then suddenly shifts direction towards the north?

Spot what is wrong here in below Picture?

The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.

Boxes are labeled but all labels are wrong!

You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.

How many such operations are necessary to correctly label the boxes?

In the four images below, can you find the odd one out?

Solve the mathematical equation in the picture below.

Your last good ping-pong ball fell into a narrow metal pipe embedded one foot deep in concrete.
How can you get it out undamaged, if all the tools you have are your tennis paddle, shoe laces, and plastic water bottle, which does not fit into the pipe?

The person who makes it has no need for it; the person who buys it has no use for it. The person who uses it can neither see nor feel it. What is it?