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

Living above a star, I do not burn
Eleven friends and they do not turn
I can just be visited in a sequence, not once or repeatedly
PQRS are my initials
Can you tell my name accurately?

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

How many minutes are there in Feb 2017?

Note: The shortest answer is the correct answer.

What am I?

Replace the question mark with the number below given a simple math problem.

John is the son of Jacob.
So,
Jacob is the_____of John's father?

Four men were in a boat on the lake. The boat turns over, and all four men sink to the bottom of the lake, yet not a single man got wet! Why?

All of the flowers I have are orchids except two. All of the flowers I have are hibiscuses except two. All of the flowers I have are roses except two.

Can you tell me how many flowers I have?

The first box has two white balls. The second box has two black balls. The third box has a white and a black ball.

Boxes are labeled but all labels are wrong!

You are allowed to open one box, pick one ball at random, see its colour and put it back into the box, without seeing the colour of the other ball.

How many such operations are necessary to correctly label the boxes?