Can you place six X (crosses) in below board without making three in a row in any way ?

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

My cousin lives in one story house in Antarctica. His house is made the of-of sandstone. what is the color of stairs?

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?

Two girls were born to the same mother, on the same day, at the same time, in the same month and year and yet they're not twins. How can this be ?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

Nine marbles are arranged in the image below. Can you slide two marbles to form a square?

A boy and his father are caught in a traffic accident, and the father dies. Immediately the boy is rushed to a hospital, suffering from injuries. But the attending surgeon at the hospital, upon seeing the boy, says 'I cannot operate. This boy is my son.' How is this situation explained?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

The King of a distant land had heard that Birbal was one of the wisest men in the East and so desired to meet Birbal. He sent Birbal an invitation to visit his country.

In due course, Birbal arrived in the distant kingdom. When he entered the palace he was flabbergasted to find not one but six kings seated there. All looked alike. All were dressed in kingly robes. Who was the real king?

The very next moment he got his answer. Confidently, he approached the king and bowed to him.

How did Birbal know who was the real king?