What brings you down but never up?

what does the below rebus means?

Two in a corner, one in a room, zero in a house, but one in a shelter. What is it?

I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

I am white when I am dirty, and black when I am clean. What am I?

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

Irene killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

Find three numbers such that

* When we multiply three numbers, we will get the prime numbers.
* The difference between the second and the first number is equal to the third and second.

Complete the series by replacing "?" with the correct number.

ST ND RD TH '?'

What famous saying does this rebus mean?

COME SERVED <---
COME SERVED
COME SERVED
COME SERVED
COME SERVED