Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

I am a type of food that is often found in the fridge and can be white in colour. What I am?
Hint 1: I am a dairy product.
Hint 2: You can spread me on the bread.

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

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?

10+10 and 11+11 can give you the same answer.

Explain how?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

Find the value of "?" in the ball picture Riddle below:

Which tank will fill first?

Akbar called Birbal and asked him to draw a line on the floor. He asked Birbal to make that line smaller without erasing it. Birbal smiled and did it before Akbar could blink his eyes.

How did he managed to do it?

You need to remove two matchsticks to make the below equation true. Can you do it ?