Why is a river so rich ?

Find out the missing number in the picture attached:

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

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

Two friends Smith and Andrew were talking about the bravery of their families. Smith told great stories about his courageous grandfather who fought for Britain in "World War I". Andrew told that his grandfather was so brave that in 1919 just after the war he was honoured with a bravery medal with the words "For our Courageous Soldiers In World War I" embedded into it. Smith knows that his friend is lying. How?

What's the only room from which no one can enter or leave

This is a simple one. You just have to count the number of Fs in the given sentence.

Finished Files are the result of years of scientific study combined with the experience of years.

How many did you count?

I have feet, but no legs. Which animal Am I?

Identify The phrase in the picture.

John was piloting a plane behind a car but was never able to overtake it. Why?