Why Aeroplane windows are round?

Can anyone tell me a word in the English dictionary which has a silent 'z'?

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?

What is the end of everything?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

Can you spot what's wrong with the following sentence?

PETER WAS ANGRY AT
HIMSELF BECAUSE HE
ACCIDENTALLY LEFT THE
THE KEYS TO HIS CAR
AT HIS FRIEND'S HOUSE.

An evil man kidnapped someone and made them take one of two pills. One was harmless, but the other was poisonous. Whichever pill the victim took, the kidnapper took the other one. The victim took their pill with water and died. The kidnapper survived. How did the kidnapper get the harmless pill?

You need to arrange three 7 and mathematical symbols to form number 1?

When is the top of a mountain similar to a savings account?

What is the next shape from answers A, B, C, and D figure?