What does the below rebus riddle means?

You are in a room with no metal objects except for two iron rods. Only one of them is a magnet.
How can you identify which one is a magnet?

What happened when the wheel was invented?

How many bananas can you eat if your stomach is empty?

What comes
Once in a Year
Twice in a Month
4 times in a Week
6 times in a Day

There was an aeroplane crash, every single person died, but two people survived. How is this possible?

Can you find a pattern and the missing number in the series given below?

100, 155, 258,? , 584, 819.

John was running from 40 thieves. John has got 3 gold boxes which weigh as 4kg, 2kg, and 1kg respectively. A witty man asked John to stay with him for seven days in exchange for 1kg gold per day. John needs to stay there for seven days and also do not want to give the witty man any advance. How can John pay for his seven days stay?

The answer I give is yes, but what I mean is no. What was the question?

It is always ahead of me yet I can never see it. What is it?