When we see 2 but call 10?

It can't be seen, can't be felt, can't be heard, and can't be smelt.
It lies behind stars and under hills, And empty holes it fills.
It comes first and follows after, Ends life, and kills laughter.
What is it?

Count the number of balls in picture below:

Which is heavier: a ton of bricks or a ton of feathers?

Jack have ten pairs of black socks, eight pairs of white socks and seven pairs of green socks. Everything is mixed in a draw. As there is no light he were not able to identify the colour of the socks. How many of the socks did he want to take to match one pair

You need to arrange three 7 and mathematical symbols to form number 1?

I am the beginning of everything, the end of everywhere. I'm the beginning of eternity, the end of time and space. What am I?

Six glasses are in a row. The first three are filled with milk and the last three are empty. By moving only one glass, can you arrange them so that the full and the empty glasses alternate?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

What has many keys but can’t open a single lock?