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
Answer:
4) a mixture.....................
Answer:
polyatomic, ionic
Explanation:
unit that contains two or more atoms covalently bonded together but that has an overall charge is called a(n) polyatomic ion. Many ionic compounds contain such units.