why number 8549176320 is one of a kind?

There are two candles. Both will only burn exactly for an hour. How will you use these two candles to measure forty-five minutes?

Begin with a word, five letters to my name,
Remove the first and last but I am the same
Take out my middle and still, I remain.
What word am I?

Get total of 120 by using five zeros 0,0,0,0,0 and any one mathematical operator.
Do you ?

What has a bottom at the top?

Find out the missing number in the picture attached:

The below given figure comprises of a pattern through which you can determine the missing letter. Can you push your mind to find the pattern and add the missing letter?

I am quite hot but become too cold if you remove the first two letters. What am I?

What has many keys but can’t open a single lock?

You are given 2 eggs.
You have access to a 100-storey building.
Eggs can be very hard or very fragile means it may break if dropped from the first floor or may not even break if dropped from 100th floor, Both eggs are identical.
You need to figure out the highest floor of a 100-storey building an egg can be dropped without breaking.
Now the question is how many drops you need to make. You are allowed to break 2 eggs in the process