What does below chemistry rebus means?

There is one four-digit whole number n, such that the last four digits of n2 are the original number n

One absent-minded ancient philosopher forgot to wind up his only clock in the house. He had no radio, TV, telephone, internet, or any other means for telling time. So he travelled on foot to his friend's place a few miles down the straight desert road. He stayed at his friend's house for the night and when he came back home, he knew how to set his clock. How did he know?

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

In the image below, you can see two glasses and two matchsticks.You need to move four matchsticks in such a manner that the crosses come inside the glasses. Note: you cannot move the crossed.

It's pretty hard to give up.
If you remove a part of it, you will be left with a bit.
Even if you remove another part, the bit still remains.
Remove one more and it still remains.

What is it?

I left my campsite and hiked south for 3 miles. Then I turned east and hiked for 3 miles. I then turned north and hiked for 3 miles, at which time I came upon a bear inside my tent eating my food! What colour was the bear?

If eleven plus two equals one, what does nine plus five equal?

Five teams were competing in cricket where they faced each other exactly once. After the tournament, the following is the point table.

DareDevils 6
SuperKings 5
Royals 4
Sunrisers 2
Riders ?

How many points did Riders end up with?

How many times can you subtract the number 5 from 25?