If you’ve got me, you want to share me; if you share me, you haven’t kept me. What am I?

Queen Elizabeth organised a royal party.

To Avoid uninvited guest royal family set a password.
Jack (an uninvited person) plan to enter the party. He stand nearby the door.

First guest comes, the security person said 'twelve' and guest replied with six.
Second guest comes , the security person said 'six' and guest replied with 'three'.

Jack thought is enough and he walked to the entry point. The security person said 'eight' , Jack replied smilingly 'four'.
He was immediately thrown out of the party. why ?

What goes up but never comes down?

The barber of Town shaves all men living in the town. No man living in the town is allowed to shave himself. The barber lives in that town. Who then shaves the barber of the town?

You have two buckets - one holds exactly 5 gallons and the other 3 gallons. How can you measure 4 gallons of water into the 5 gallon bucket?

(Assume you have an unlimited supply of water and that there are no measurement markings of any kind on the buckets.)

What is the coolest letter in the alphabet?

How high do you have to count before you use the letter “a” in the English spelling of the whole number?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

What brings you down but never up?

John named his first son Alpha, second Beta, third Charlie and fourth Delta. What is the fifth son's name?