CBSE Class 9 Science Structure of atom Sure Shot Questions B

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1. Which of the following correctly represent the electronic distribution in the Mg atom?

(a) 3, 8, 1 (b) 2, 8, 2 (c) 1, 8, 3 (d) 8, 2, 2

2. Rutherford’s ‘alpha (α) particles scattering experiment’ resulted in to discovery of

(a) Electron (b) Proton (c) Nucleus in the atom (d) Atomic mass

3. The ion of an element has 3 positive charges. Mass number of the atom is 27 and the number of neutrons is 14. What is the number of electrons in the ion?

(a) 13 (b) 10 (c) 14 (d) 16

4. Elements with valency 1 are

(a) Always metals (b) always metalloids

(c) either metals or non-metals (d) always non-metals

5. The first model of an atom was given by

(a) N. Bohr (b) E. Goldstein

(c) Rutherford (d) J.J. Thomson

6. Is it possible for the atom of an element to have one electron, one proton and no neutron? If so, name the element.

7. Why did Rutherford select a gold foil in his α–ray scattering experiment?

8. Will Cl-35 and Cl-37 have different valences?

9. Calculate the number of neutrons present in the nucleus of an element X which is represented as 31 X15 .

10. The atomic number of calcium and argon are 20 and 18 respectively, but the mass number of both these elements is 40. What is the name given to such a pair of elements?

11. Why do Helium, Neon and Argon have a zero valency?

12. In what way the Rutherford proposed atomic model?

13. In what way the Thomson proposed atomic model?

14. What were the drawbacks of Rutherford’s model of an atom?

15. What are the limitations of J.J. Thomson’s model of an atom?

16. In television picture tube which type of rays are used?

17. Which is heavier, neutron or proton?

18. If electrons move from K to L shell, will the energy be absorbed or evolved?

19. Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have?

20. An ion X 2⁺ contains 18 electrons and 20 neutrons. Calculate the atomic number and mass no. of element X. Name the element X.

21. Give one Achievement and one limitation of J.J Thomson’s model of atom?

22. In a given electric field, β- particles are deflected more than α- particles inspite of the fact that α - particles have larger charge, why?

23. What are valence electrons? What is their significance?

24. What would be the observation if the α - particle scattering experiment is carried out usinga foil of a metal other than gold?

25. Electronic configuration of Potassium is 2,8,8,1 and Calcium 2,8,8,2, when M shell can have maximum of 18 electrons then why next element Scandium has electronic configuration 2,8,9,2 and not 2,8,8,3 ?

26. What are isotopes and Isobars? What are two isotopes of chlorine? Calculate the average atomic mass of a chlorine atom?

27. What is present concept of an atom? Explain in detail? Why this model is considered to be the most appropriate model?

28. Explain the Rutherford’s alpha particle scattering experiment. What were the main conclusions drawn from this experiment?

29. A naturally occurring sample of :-

(i) 69.2% of 53Cu& 30.8% of 65Cu. Find the average atomic mass of a naturally occuring sample of copper.

(ii)7.42% of 6Li & 92.58% of 7Li.Find the average atomic mass of a naturally occuring sample of Lithium.

30. Calculate the no. of atoms of each element persent in 9.8 g of sulphuric acid, H2SO4. (H=1, S=32, O=16)

31. How to calculate the atomicity and the atomic mass of an atom?

32. To weight BaCl2 or Na2SO4

a) use a polythene bags and spring balance

b) use a watch glass and spring balance

c) use a polythene bags and physical balance

d) use a watch glass and physical balance

33. To weight sodium sulphate or barium chloride it should be in form ofa) saturated solution b) large crystals c) small crystals d) fine powder

34. What is the distribution of electrons in an atom of Phosphorus and how can it have two valencies

35. The maximum no. of electrons present in shell is given by the formula 2n2and themaximum no. of electrons filled in M shell is 18. But in the element calcium we only fill 8 electrons in the M shell and move on to the N shell. why ?

36. What are alpha particles?

37. Write ddifference between atomic mass and mass number?

38. An ion (M2+) contain 10 electrons and 12 neutrons what is the atomic number and mass number of the element M.

39. An ion M3+ contains 10 electrons and 14 neutrons. What are the atomic mass and mass number of the element M ? Name the element.

40. 10 gm of silver nitrate solution is added to 10 gm of sodium chloride solution. What change in mass do you expect after the reaction and why?

41. Write the atomicity of the following molecules: (i) H2SO4 (ii) CCl4

42. Define the term mole.

43. What is the law of constant proportions?

44. What is molar mass? What are its units?

45. Define atomicity.

46. Calculate the formula unit mass of Na2CO3. [Atomic mass of Na = 23 u, C = 12 u, O = 16 u]

47. Give the definition of a cation and an anion.

48. An element X has a valency 3. Write the formula of its oxide.

49. Calculate the number of moles is 52 g of He (Helium)

50. If 12 gm of carbon is burnt in the presence of 32 gm of oxygen, how much carbon dioxide will be formed ?

51. Calculate the number of moles in 17 gm of H2O2. (Atomic weight of H = 1 u, O = 16 u).

52. Define and explain atomic mass of an element.

53. If one mole of carbon atoms weighs 12 g. What is the mass of 1 atom of carbon ?

54. Calculate the mass of 1 molecule of oxygen gas.

55. The mass of single atom of an element is 2.65 × 10–23 g. Calculate its atomic mass. [NA = 6.022 × 1023 mol-1 ]

56. Calculate percentage composition of glucose (C6H12O6).

57. John placed 10 moles of sulphur molecules (S8) and 5 moles of glucose (C6H12O6) in thetwo different pans of a physical balance. Find which pan of the balance would be heavier,support your answer with calculations. (atomic mass : O = 16 u, C = 12 u, H = 1 u, S = 32 u)

58. What is Avogadro constant ?

59. Calculate the number of particles present in 56 gm of N2 molecule.

60. Calculate the number of moles present in (a) 60 g of calcium. (b) 3.011 × 1023 number of oxygen atoms. [Given that Ca = 40u; Avogadro number, NA = 6.022 × 1023 per mole]

61. Give an account of the ‘mole concept’.

62. Calculate the ratio by number of atoms for Magnesium sulphide.

63. (a) The average atomic mass of a sample of an element X is 35.5u. What are the percentages of isotopes 37 35 17 X and 17 X in the sample ?

(b) Write any two applications of isotopes.

64. Nitu presented a silver lamp to her mother on her birthday. The lamp contained 3.011 ×1023 atoms of silver in it. What is the mass of silver lamp and the cost of it if 1 gm silver costs Rs 60. Atomic mass of Ag = 108 u, N0 = 6.022 × 1023 per mole.

65. Verify by calculating that 5 mole of CO2 and 5 mole of H2S do not have the same mass. (Atomic mass of C = 12 u, O = 16 u, H = 1 u, S = 32 u)

66. A solution is made by dissolving sodium chloride in water and its concentration is expressed as 0.9% by mass. Calculate : (i) the number of moles, and (ii) number of molecules present in NaCl for this solution. [Given : mass % = (Mass of solute×100)/ Mass of solution](Atomic mass of Na = 23.0 u, Cl = 35.5 u)

67. (i) What do the following symbols / formulae stand for :

(a) 2O (b) O2 (c) O3 (d) H2O

(ii) Give the chemical formula of the following compounds :

(a) Potassium carbonate (b) Calcium chloride

(iii) Calculate the formula unit mass of Al2(SO4)3.

(Given : Atomic mass of Al = 27 u, S = 32 u, O = 16 u)

68. An element 147 A exists as diatomic gas in nature which is relatively inert and forms 78% of earth’s atmosphere.

(a) Identify the gas and write its molecular formula. Write the formulae of its nitrite and nitrate ions.

(b) How many moles of this gas would contain 12.044 × 1023 atoms of this element ? (Avogadro’s no. = 6.022 × 1023)

(c) Calculate the molecular mass of (a) NH4 NO3 and (b) HNO3

(Given atomic masses N = 14 u, O = 16 u, H = 1u)

69. (a) In ammonia, nitrogen and hydrogen are always present in the ratio 14 : 3 by mass. State the law which explains the above statement.

(b) During the formation of ammonia, what mass of hydrogen gas would be required to

react completely with 42 g of nitrogen gas ?

70. (a) Calculate the number of moles in 112 g of iron.

(b) Calculate the mass of 0.5 moles of sugar (C12H22O11).

(c) Define the term molecular mass.

(d) Determine the molecular mass of ZnSO4.

[Atomic mass of Zn = 65 u, S = 32 u, O = 16 u]

(e) Calculate the number of molecules of carbon dioxide, present in 4.4 g of CO2.

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