What breaks yet never falls, and what falls yet never breaks?

Which number should replace the question mark?

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?

If an electric train is travelling south, then which way is the smoke going?

Can you solve the maths in the below-given picture equation?

How is a fly different from a mosquito?

I make two people out of one. What am I?

What does this rebus mean?

O
N
C
E
TIME

Suppose that you are trapped on the surface of a frozen lake. The surface is so smooth and ideal that there is no friction at all. You cant make any grip on the ice and no wind is blowing to help you out. You have just a mobile phone with you which has got no reception disabling you to call for help.

How will you plan your escape before you freeze to death on the frozen lake?

I have some blue and red sock in my drawer. I have a total of 4 socks. I pick 2 socks and the chance that I get a pair of red socks is 1/2.

What is the chance of picking a pair of blue socks?