Isotopes= a group of atoms with the same no. of protons , but different no. of neutrons
Hydrogen isotopes

The name of the second isotope is deuterium and the name of the third isotope is tritium(radioactive).The most abundant isotope is
Density will be mass/volume= 0.2/500 = 0.0004
I've actually used the magnet test to determine if a gold necklace of mine was real or not. If the gold item aka the crown is attracted to a magnet, it is definitely not real gold.if it isn't then its real gold.