What's the only room from which no one can enter or leave

I was born in a small house and I live in it all alone. No windows and no doors have been assigned to my house. The only way I can go out is by breaking through the walls of my house.

Who am I?

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

There are 100 bulbs in a room. 100 strangers have been accumulated in the adjacent room. The first one goes and lights up every bulb. The second one goes and switches off all the even-numbered bulbs - second, fourth, sixth... and so on. The third one goes and reverses the current position of every third bulb (third, sixth, ninth? and so on.) i.e. if the bulb is lit, he switches it off and if the bulb is off, he switches it on. All the 100 strangers progress similarly.

After the last person has done what he wanted, which bulbs will be lit and which ones will be switched off?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

A donkey is behind another donkey
I'm behind that second donkey
But there is a whole nation behind me

It is a murder you can describe in a word.

There's one "sport" in which neither the spectators nor the participants know the score or the leader until the contest ends.

What is it?

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

What English word has three consecutive double letters?

A four-digit number (not beginning with 0) can be represented by ABCD. There is one number such that ABCD=A^B*C^D, where A^B means A raised to the B power. Can you find it?