What is the word or phrase?

What is both possible and impossible at the same time?

When it's bad luck to meet a black cat?

Before Mount Everest was discovered, what was the highest mountain in the world?

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?

Can you find out a way through which you can make five squares out of the given figure by moving just six match sticks?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

Christina is practising her dance steps along with her friends. In a particular sequence, all of them form a row. At that point, Niharika is standing in the 4th position from either end of the row.
Can you find out how many girls are practising together?

In the given picture, you can find two letters missing. When two particular letters are placed in the missing spots, you get an eight-letter word while reading in the anti-clockwise direction. Can you find out the missing letters and the missing word eventually?

Find the number of squares in the below-given picture.