Aiezsedai

Hi, My question is about salinity of seas. Why is the Red Sea (45 promilles) saltier than the World Ocean (35 promilles)? And why is the Dead Sea even saltier - 67 promilles? What are the natural causes of these differences?

Why in the troposphere the temperature is falling? I can't understand generally what causes the temperature to fall with the altitude. Maybe it is something related to the amount of gases. Thank you for your help!

Why the atmosphere is thinner over the poles (600km) while the average is 800km? Is it thicker somewhere else and what's the reason for this? Thank you for your help! This is something that I didn't understand during my geography class.

What is a point charge? I read that it is hypothetical an it hasn`t got any dimensions, length, etc. The article even mentioned that for that reason its density is infinite. I am really confused. Could you please explain to a beginner? Is it a charge smaller than an electron and what do they use it for?