Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

I had an infinite supply of water and 5 litres and 3 litres jars.

How would you measure exactly 4 litres in the least number of steps?

What makes this number unique: 8,549,176,320?

When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

I hide my treasure in the ground, my tail is big and fluffy. If you spot me in a tree, please don’t call me scruffy. What am I?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

You have to put a letter on the following to make it a meaningful word. The only challenge is that you can't use 'E'.

S E Q U E N C _

I am a normal creature, but I have five hands. I can even have more but even then I will be considered normal.

Who am I?

I am the fastest animal but cannot climb the tree. What am I?

How many triangles can you count in the figure given?