What are the different forms of same element with different molecular structures?

An object has a weight of 500 on earth what is the mass of this object

Which statement is the best definition of an atom? a) anything that has mass and occupies space. b) the smallest particle that has the properties of an element. c) a substance that cannot be broken down chemically into simpler substances. eliminate d) the smallest unit of a substance that exhibits all of the properties characteristic of that substance.

Can a molecule have bond dipoles but not have a molecular dipole?