What information do you get from the Fig. 4.4 about the atomic number, mass number and valency of atoms X, Y and Z? Give your answer in a tabular form.

The atomic number of element X is 5. Its mass number is 5 Protons + 6 Neutrons= 11. Since, there are 3 electrons in the outermost shell, its valency is 3. Atom X can lose 3 electrons to attain the nearest noble gas configuration.

The atomic number of atom Y is 8. Its mass number is 8 protons + 10 neutrons = 18. It has 6 electrons in the outermost shell. In order, to attain the nearest noble gas configuration, it has to gain 2 electrons. Therefore, the valency of atom Y is 2.

The atomic number of Z is 15. The mass number is equal to 15 protons + 16 neutrons = 31. The outermost shell has 5 electrons. To attain the nearest noble gas configuration, atom Z can either gain or lose electrons. It can gain 3 electrons and become negative ion with -3 charge or it can also lose 5 electrons and result in a positive ion with +5 charge. As a result, atom Z can show a valency of both 3 and 5.