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

Look at the picture and find out which square is not linked with any of the other squares.

A patient was diagnosed with some ailment. He was given five different tablets to take at night at an interval of 15 minutes.

How long will it take the patient to consume all the five tablets?

I travel all around the world but always stay in the corner. What am I?

What is the centre of gravity?

10 people came into a hotel with 9 rooms and each guest wanted his own room. The bellboy solved this problem.
He asked the tenth guest to wait for a little with the first guest in room number 1. So in the first room, there were two people. The bellboy took the third guest to room number 2, the fourth to number 3, ..., and the ninth guest to room number 8. Then he returned to room number 1 and took the tenth guest to room number 9, still vacant.
How can everybody have his own room?

What number when divided in half becomes zero?

2, 3, 5, 9, 17, _ What is the next number in the sequence?

What breaks yet never falls, and what falls yet never breaks?

There are are five things wrong with this sentence; only geniuses will be able to to spot all of the mitstakes