Before Mount Everest was discovered, what was the highest mountain in the world?

What can run but never walk, have a mouth that never speaks, have a head that never weeps, and have a bed but never sleeps?

I am looking for a word that change both gender and number when i add the letter 'S'.

What Word am I Looking For ?

How can you write nineteen in a manner that if we take out one, it becomes twenty?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see?

Can you find the missing piece of the Porsche?

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

I look flat, but I am deep. Hidden realms I shelter. Lives I take, but the food I offer. At times I am beautiful. I can be calm, angry, and turbulent. I have no heart but offer pleasure as well as death. No man can own me, yet I encompass what all men must have. What am I?

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 a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.