What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

I have nine bottles of wine and one of the nine bottles is poisoned.
I need to find the poisoned bottle with two facts
(1) Poison is deadly, only a sip will cost death
(2) I have two mice to do so.

How should I do it?

Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

What does the following represent?

N N N N N N N

A A A A A A A

C C C C C C C

John is asked to stand behind Jacob and Jacob is asked to stand behind John. Both of them feel confused about it and don't know what to do?

But it is quite possible, do you know how?

The person who makes it has no need for it. He who purchases it does not use it. The person who does use it does not know they are. What is it?

A man dies of old age on his 25 birthday. How is this possible?

You are given four results as below:
1111 = F
2222 = E
3333 = T
Then, can you find out how to code 4444?

If,

20 % 5 = 24

21 % 7 = 33

42 % 6 = 67

Then;

66 % 6 = ?

I am white when I am dirty, and black when I am clean. What am I?