Use only one mathematical symbol and all numbers (0-9) to get a sum of 99

Name a key which is hardest to turn.

You have two buckets of 11 liters and 6 litres.
How can you measure exactly 8 litres?

Can you find the company name in the pictogram below?

John was working on a Chemical Mixture whose weight comprise 90% liquid and 10% solid. The total weight of the mixture is 20 pounds. After a while, John noticed that some of the liquid evaporated and now the liquid comprises just 50% of the weight.

What is the weight of the chemical mixture now?

Can you decode the below cypher?

896983327332676578

I am an eight letter word and I am a computer terminology.
The second, third and fourth letters make an animal.
The fourth, fifth, sixth, seventh and eighth letters make a weapon.
The first, second, third and fourth letters can be taken as an outcome of any exam.
The fifth, sixth, seventh and eighth letter combine to form a high end typing software.

Can you tell who am I ?

Can you find the mistake in the below statement?

What is both possible and impossible at the same time?

Christina is practising her dance steps along with her friends. In a particular sequence, all of them form a row. At that point, Niharika is standing in the 4th position from either end of the row.
Can you find out how many girls are practising together?