Not necessarily.
{John, 1, red, monitor} is a perfectly valid set.
They are alike because some are made out of the same elements.
neutrons of all atoms are alike
They are all Elements and They are diiferent substances
the number of protons
The chemical elements in a group have similar properties.
Both are composed from chemical elements.
Compound or substance: a molecule containing two or more types of chemical elements.
A null or empty set is a set that does not contain any elements.
null set or empty set, is a set with no elements.
its when too atoms are alike
All chemical elements are formed from protons, neutrons (excepting H-1) and electrons.
Compound are all alike because they all have two elements combined together like iron+sulfide=ironsulfide