What is the most difficult thing in chemistry to learn?

After cloud droplets form, what must happen to them for precipitation to occur?

Suppose you have designed a new thermometer called the x thermometer. on the x scale the boiling point of water is 129 ? x and the freezing point of water is 13 ? x. part a at what temperature are the readings on the fahrenheit and x thermometers the same?

In what environment would mineral formation caused by high pressures and high temperatures most likely occur?