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

In a mathematical quiz, you are asked the following question:

Use three 9s in a mathematical expression without dividing or multiplying to form the number one.

Can you answer the question?

I know a ten-letter word in the English language which can be typed using only the top rows of the computer keyboard.

I had an infinite supply of water and 5 litres and 3 litres jars.

How would you measure exactly 4 litres in the least number of steps?

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

I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter. What am I?

A man was driving a black truck. His lights were not on. The moon was not out. A lady was crossing the street. How did the man see her?

What does this simple rebus mean?

Find the Odd One Out?
84129
32418
47632
36119
67626
72927

You stand in front of two doors. A guard stands next to each door. You know the following things: one path leads to paradise, the other leads to death. You cannot distinguish between the two doors. You also know that one of the two guards always tells the truth and the other always lies. You have permission to ask one guard one question to discover which door leads to paradise. What one question would you ask to guarantee you enter the door to paradise?