If you say my name, I will no longer exist. What am I?

There is a five-letter word which has 3 consonants(all are same) and 2 different vowels.
Also, something wrong is associated with the word.

Can you name it?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

A person was found dead on a big green land with no trees or buildings around. When the police arrived, they found a piece of rock lying next to him and the man was wearing clothes comprising of red, blue and yellow colours.

Can you tell who the person is and what was the cause of death?

Which tank will fill first?

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?

John enters a small room. The Door Closes.
When the door opens, John is in a larger room.

Explain?

The average age of 10 members of a committee is the same as it was 4 years ago, because an old member has been replaced by a young member. Find how much younger is the new member ?

I am a white box having no key or lid.
Yet there is a golden treasure inside it.

What Am I?

What is both possible and impossible at the same time?