Explain with examples: (i) Atomic number (ii) Mass number, (iii) Isotopes and (iv) Isobars. Give any two uses of isotopes.
(i) Atomic number: The atomic number of an element is equal to the number of protons in the nucleus of its atom. e.g., Oxygen has 6 protons hence atomic no. = 6. (ii) Maas number: The mass number of an atom is equal to the number of protons and neutrons in its nucleus. Nucleons = number of protons + number of neutrons Example: Protons + Neutrons = Nucleus = Mass number 6 + 6 = 12 (iii)Isotopes: Isotopes are atoms of the same element which have different mass number but same atomic number.  (iv)Isobars: Isobars are atoms having the same mass number but riifteren atomic numbers.  Both calcium and argon have same mass number but different storm number. Two uses of isotopes are: (i) An isotope of iodine is used in the treatment of goitre. (ii) An isotope of uranium is used as a fuel in nuclear reactors.
