CBSE class XII Chemistry Important Questions 2008



Q. 1. There is a considerable increase in covalent radius from N to P but from As to Bi only a small change is observed.

Q. 2. Ionisation enthalpy of group 15 elements is much higher than that of group 14 elements.

Q. 3. Ionic radius of Sb and Bi are very less when compared to the ionic radius of N,P and As.

Q. .4. Metallic character of group 15 elements decreases on going down the group.

Q. .5. Tendency to show – 3 oxidation states in group 15 decreases on going down the group.

Q. .6. Nitrogen can’t form penta halides.

Q. 7. Nitrogen exhibits bonding while heavier members exhibit bonding.

Q. 8. N2 is a gas while P4 is a solid.

Q. 9. Catenation tendency is weaker in nitrogen.

Q. 10. N2 molecule is chemically inert while white phosphorus is more reactive.

Q. 11. In group 15, +3 oxidation state is more stable than +5 oxidation state on going down the group .

Q. 12. R3 P=O is known but R3 N=O is unknown.

Q. 13. Basicity of hydrides NH3> PH3 > AsH3 > SbH3 > BiH3

Q. 14. Stability of hydrides NH3> PH3 > AsH3 > SbH3 > BiH3

Q. 15. Reducing character of hydrides NH3<>3 <>3 <>3 3

Q. 16. The oxides in higher oxidation states of group 15 elements are more acidic than that of lower oxidation state.

Q. 17. Basicity of group 15 oxides increases on going down the group.

Q. 18. PCl5 is more covalent than PCl3.

Q. 19. PCl5 is more covalent than PF5.

Q. 20. All the five bonds in PCl5 are not equivalent.(Or) PCl5 is more reactive than PCl3.

Q. 21. Both PCl3 and PCl5 fumes in air.

Q. 22. PH3 has lower boiling point than NH3.

Q. 23. NH3 acts as a lewis base.

Q. 24. NO2 molecule dimerise to become N2O4.

Q. 25. Aluminium is rendered passive in concentrated HNO3.

Q. 26. Concentrated HNO3 becomes yellow when exposed to light.(Or) concentrated HNO3 is an oxidizing agent.

Q. 27. White phosphorus is more reactive than red phosphorus. Black phosphorus is least reactive.

Q. 28. Bond angle in PH3+ is higher than that of PH3.

Q. 29. HNH bond angle in NH3 is less than the tetra hedral bond angle of 109.50.

Q. 30. Bond angles of HPH,HAsH and HSbH are closer to 900.

Q. 31. H3PO4 is tri protic, H3PO3 is diprotic while H3PO2 is mono protic.

Q. 32. H3PO2 is a good reducing agent.

Q. 33. H3PO2 is a stronger reducing agent than H3PO3.

Q. 34. NO is an odd electron molecule but does not dimerise to give N2O2.

Q. 35. Sulphur has very high boiling and melting point when compared to oxygen.

Q. 36. In group 16 tendencies to show -2 oxidation state decreases on going down the group.

Q. 37. In group 16 +4 oxidation state become more stable than +6 oxidation state on going down the group.

Q. 38. Oxygen can show a maximum covalency of 4 and it can not form hexa valent compound.

Q. 39. Acidity of group 16 hydrides H2O 2 S <>2Se <>2Te.

Q. 40. Reducing character of group 16 hydrides H2O 2 S <>2Se <>2Te

Q. 41. Boiling point of H2O is higher than that of H2 S.

Q. 42. Sulphur exhibit +6 oxidation state when it combines with fluorine.

Q. 43. SF6 is exceptionally stable or it can not be hydrolysed easily.

Q. 44. SF6 is known while SCl6 is unknown.

Q. 45. SF6 is known while SH6 is unknown.

Q. 46. H2O is a liquid while H2S is a gas.

Q. 47. MnO is basic while Mn2O7 is acidic.

Q. 48. O3 is thermo dynamically unstable than O2 (or) . O3 in higher concentration is explosive.

Q. 49. NO gas depletes ozone layer.

Q. 50. Sulphur in vapour state is paramagnetic.

Q. 51. HCl and HNO3 are prepared by reacting NaCl and NaNO3 respectively with H2SO4 while HBr and HI can’t be prepared by this method.

Q. 52. Cane sugar chars in concentrated sulphuric acid.

Q. 53. Concentrated sulphuric acid is a good oxidizing agent.

Q. 54. Two S-O bonds in SO2 are equivalent.

Q. 55. Ka2 of H2SO4 is <<>1.

Q. 56. Halogens have maximum negative electron gain enthalpy in each period.

Q. 57. Fluorine has lesser negative value of electron gain enthalpy than chlorine.

Q. 58. All halogens are colored.

Q. 59. F2 has smaller enthalpy of dissociation than Cl2.

Q. 60. Fluorine has lesser negative value of electron gain enthalpy than chlorine but fluorine is a stronger oxidizing agent than chlorine.

Q. 61. Fluorine shows only – 1 oxidation state. Other halogens can exhibit positive oxidation state.

Q. 62. Halogens show positive oxidation state when they combine with oxygen and fluorine atoms.

Q. 63. Halogens are good oxidizing agent and oxidizing power (reactivity) decreases with the increase in atomic number.

Q. 64. Most of reactions of fluorine are exothermic.

Q. 65. HF is a liquid while other hydrogen halides are gases.

Q. 66. HF has highest boiling point while HCl has lowest boiling point among hydrogen halides.

Q. 67. Acidity of hydrogen halides HF <>

Q. 68. Thermal stability of hydrogen halides HF > HCl > HBr > HI

Q. 69. Thermal stability of group 16 hydrides H6O > H6S > H6Se > H6Te

Q. 70. OF2 is fluoride of oxygen and not oxide of fluorine.

Q. 71. Oxygen and chlorine has similar electro negativity. Oxygen form hydrogen bonding but not chlorine.

Q. 72. .Ionic character of halides MF>MCl>MBr>MI

Q. 73. Electron gain enthalpy of O O- is – 141 KJ/mole and O O --> O2- is + 702 KJ/mole. Large number of oxides having O2- is known and not O-.

Q. 74. In metal halides, halides in higher oxidation state of the metal is more covalent than the one in lower oxidation state.(PbCl4 is more covalent than PbCl2)

Q. 75. Inter halogen compound is more reactive than the halogens from which it is formed.

Q. 76. Chlorine is a powerful bleaching agent.

Q. 77. HCl reacts with Fe to give FeCl2 and not FeCl3

Q. 78. Fluorine forms only one oxo acid HOF

Q. 79. Acidity of oxo acids HClO4> HClO3> HClO2> HC1O.

Q. 80. Acidity of oxo acids HOCl>HOBr>HOI

Q. 81. Oxidizing power of HClO4> HClO3> HClO2> HClO

Q. 82. Fluorine form fluoride of oxygen while other halogens form oxides of halogen.

Q. 83. Group 18 elements are chemically unreactive.

Q. 84. Group 18 elements have very high ionization enthalpy and it decreases on going down the group.

Q. 85. Group 18 elements have positive value of electron gain enthalpy.

Q. 86. Group 18 elements have lower value of boiling and melting point and it increases on going down the group.

Q. 87. Group 18 elements have larger atomic radius.

Q. 88. Bartlett synthesized XePtF6 from his knowledge of earlier known compound O2PtF6.

Q. 89. Xenon forms noble gas compounds.

Q. 90. Xenon forms compounds only with oxygen and fluorine.

Q. 91. Helium is used in diving apparatus.

Q. 92. Oxygen has lesser negative value of electron gain enthalpy than Sulphur.

 

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