Replace the question mark with the correct number in the below-given picture?

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

Can you find out which options fits best with the missing column?

I am written with two letters.
I said with the one.
I usually am seen with the two.

Who am I?

P is the father of Q and S is the son of R. T is the brother of P and has a daughter U. If R is the sister of P, then what is the relation between U, Q and S?

How can you make number one disappear by adding something to it?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see? What is it?

Intelligence Agency need to break the vault but the problem is that they are not able to break the vault.

On the vault, a text is written as:

31 11 33 33 43 45
21 25
31 24 11 31 51 41

To Break the code Intelligence Agency brings a mathematician named Joseph.
Minutes later he deciphers the code.

Whats the code?

They do not possess flesh or feathers or scales or bone
But still, they are blessed with fingers and thumbs of their own.

I have lakes with no water, mountains with no stone and cities with no buildings. What am I?