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QUESTIONS BANK CBSE BOARD PAPER  Questions:   If K and L shells of an atom are full, then what would be the total number of electrons in the atom ? What is the valency of this element ? Questions:   List three main features of Rutherford�s nuclear model of an atom. Questions:   On the basis of the number of protons, neutrons and electrons in the samples given below identify    (a) the cation     (b) the pair of isobars and            (c) the pair of isotopes. Sample Protons Neutrons Electrons A 17 18 16 B 18 19 18 C 17 20 17 D 17 17 17 Questions:   Composition of the nuclei of two atomic species A and B are given as under : Particala A B Protons 17 17 Neutrons 18 20 (i) What are the mass numbers of A and B ?    (ii) How are they related to each other ? Questions:   (i) Draw a sketch of Bohr�s model of an atom with three shells...

Questions:    Explain with examples (i) atomic number (ii) mass number (iii) isotopes and (iv) isobars.  Give any two uses of isotopes. Ans. (i) Atomic number : The number of protons in the nucleus of an atom is called its atomic number. Example : Chlorine has 17 protons in its nucleus, therefore, its atomic number is 17. (ii) Mass number : The number of protons and neutrons present in the nucleus of an atom is known as its mass number. Example : Sodium has 11 protons and 12 neutrons in its nucleus, therefore, its mass number is (11 + 12) = 23. (iii) Isotopes : Atoms of the same element having the same atomic number but different mass numbers are called isotopes. Example : Chlorine has two isotopes 35 17 Cl and 37 17 Cl , in which atomic number is 17 for both, but mass numbers are 35 and 37. (iv) Isobars : Atoms of different elements having the same mass number, but different atomic numbers are known as isobars. Example : Calcium and argon atoms have the same mass number ...