What number when divided in half becomes zero?

I have one of the three numbers: 1, 2, or 3 in my mind. I speak only truth. You can ask me just one question for which I will only reply in yes or no or don't know. What question will you ask from me so that you are able to know the number?

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

What has one eye, but can’t see?

In the image given, you can find several triangles. Can you count them all?

On a charity event in Russia, Murray beat Djokovic by winning six games and losing three games.
Note: There is a total of 5 service breaks(one who serve lost the game).
Who served first, Djokovic or Murray?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

Find the number of squares in the below picture

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

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10