The most water on earth is held by the oceans .
the number of protons and the number of neutrons determine an element's mass number. :D
Physical change
iron nail have high melting point, thus, when it is heated, it will not melt very easily.
chemical change
iron nail can rust due to the exposure to the air(oxygen). iron in the nail and oxygen in the air will react together to form iron oxide(rust).
furthermore, the reaction is irreversible.
DNA, which is found in chromosomes in the nucleus
