What is the basis for dividing the atmosphere four layers?

How do you identify the anode on a power source such as a battery? how do you identify the cathode? how are terms anion and cation?

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

Astring vibrates with a frequency of 10 hz. why can't a person hear the sound waves produced by the vibrating string, no matter how large the amplitude of the waves? out! this is homework and due tomorrow! you so much!