Explain with examples(i) Atomic number,(ii) Mass number,(iii) Isotopes andiv) Isobars.Give any two uses of isotopes.

(i) Atomic Number: The atomic number of an element is defined as the number of protons present in the nucleus of an atom of that element. It is denoted by the symbol 'Z'. For example, the atomic number of hydrogen is 1 because there is one proton in the nucleus of a hydrogen atom.

(ii) Mass Number: The mass number of an atom is the total number of protons and neutrons in the nucleus. It is denoted by the symbol 'A'. For example, the mass number of helium is 4 because there are 2 protons and 2 neutrons in the nucleus of a helium atom.

(iii) Isotopes: Isotopes are atoms of the same element that have the same atomic number but different mass numbers. This is because they have the same number of protons but different numbers of neutrons. For example, carbon-12 and carbon-14 are isotopes of carbon. They both have 6 protons (so their atomic number is 6) but carbon-12 has 6 neutrons and carbon-14 has 8 neutrons.

(iv) Isobars: Isobars are atoms that have the same mass number but different atomic numbers. This means they have the same total number of protons and neutrons, but a different number of protons. For example, argon-40 and potassium-40 are isobars. They both have a mass number of 40, but argon has 18 protons and potassium has 19 protons.

Uses of Isotopes:

1. Medical Use: Certain isotopes are used in medicine for diagnostic and treatment purposes. For example, iodine-131 is used to treat thyroid cancer and to diagnose thyroid disorders.

2. Archaeological Use: Isotopes like carbon-14 are used in radiocarbon dating. This technique is used by archaeologists to determine the age of artifacts and fossils, by measuring the amount of carbon-14 they contain.