CBSE Important Questions Chemistry Class XII 2009

Important Questions


Class XII


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, H3PO3is 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 H2O2 S <>2Se <>2Te.

Q. 40. Reducing character of group 16 hydrides H2O2 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. SF6is 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.

Q. 93. What type of defect reduces the density of unit cell?

Q. 94. What is the effect of temperature on osmatic pressure of the solution?

Q. 95. Determine the order of the reaction if its half life is inversely proportional to theinitial concentration of the reactant.

Q. 96. Mention two uses of formaldehyde.

Q. 97. Write the IUPAC name of the compound CH3 OCOCH2 CH2 COO CH3

Q. 98. What do you understand by radial probability function 4pr2R2? Draw theradial probability function curve for 2s and 2p orbital.

Q. 99. Comment on the validity of the following statements:

  1. A reaction with DG0<>
  2. An exothermic reaction is always spontaneous.

Q. 100. The outer electronic configuration of two elements of lanthanoids are given below

  1. 4f1 5d1 6s2
  2. 4f7 5d0 6s2. Determine the atomic number of these elements.

Determine the stable oxidation state of these elements.

Q. 101. Give two differences between conformational isomerism and configurational isomerism.

OR A compound having two chiral centers does not always have four stereo isomers. Justify this statement with a suitable example.

Q. 102. Mention the differences between thermo setting and thermo plastic polymers.

Q. 103. Distinguish chemically between

  1. Phenol and methanol
  2. Propan-1-ol andpropan-2-ol.

Q. 104. Complete the following chemical equations:

  1. U+ClF3®
  2. Ca3(PO4)2 +SiO2 +C®

Q. 105. Write the ground state electronic configuration of N2.

  1. Determine the bond order of N2.
  2. N2 and CO has same bond order, but CO is more reactive than N2. Why?

Q. 106. An element A crystallizes in FCC structure. 200g of this element has 24x1023 atoms. Density of unit cell is 7.2g/cm3. Calculate the radius of A. Avagadro number= 6x 1023 mole- 1

Q. 107. The activation energy of a first order reaction at 270C is 54 KJ/mole. Activation energy of the same reaction at the same temperature in the presence of a catalyst is 44 KJ/mole. How many times the reaction rate changes in the presence of catalyst at this temperature? (R=8.314J/K/mole)

Q. 108. 0.85% solution of NaNO3 is 90% dissociated at 300K.Determine the osmatic pressure of the solution.( R= 0.0821 L atm/K/mole. Molar mass of NaNO3=85u) OR Determine the boiling point of 1M solution of KCl. Assume that KCl is 90% dissociated. Density of KCl solution is 1.05g/cm3. Molar mass of KCl=74.5u. Kb= 0.52 K Kg mole- 1

Q. 109.

  1. Predict the sign of entropy change for the reaction
    CaCO3(s)®CaO(s) +CO2(g)
  2. You are provided with the following DrG0 values
    S2 +2 O2 ® 2SO2 DrG0 = - 544 KJ/mole
    2Zn +O2® 2ZnO DrG0 = - 480 KJ/mole
    2Zn+ S2 ® 2ZnS DrG0 = - 293 KJ/mole

Show that roasting of ZnS to ZnO is a spontaneous process.

Q. 110. Explain the terms activity and selectivity of catalyst with examples.

Q. 111

  1. How is potassium dichromate prepared from chromite ore?
  2. Write the ionic equation of the reaction involved when KMnO4 is treated withferrous sulphate solution in acid medium.

Q. 112. Using Valence bond theory compare the structure and magnetic behavior of

  1. Ni (CO)4
  2. [Ni (CN)4]2- Atomic number of Ni=28

Q. 113.

  1. A radio active element of group 18 undergoes a decay. Determine the position ofthe new nuclide.
  2. Calculate the mass of 140 La in a sample whose activity is 3.7x1010Bq. Given half life of 140 La = 40 hours.

Q. 114. Carry out the following conversions:

  1. Benzoyl chloride to benzaldehyde.
  2. Hex-1-ene to pentanal
  3. Hexane nitrile to 1-amino pentane.

Q. 115. Account for the following:

  1. In ammonalysis of halo alkanes primary amine is the only product when NH3is taken in large excess.
  2. Tert amine has lower boiling point than primary amine of comparable molarmass,
  3. Amide formed in acylation reaction of amine, does not react further withacid halide.

Q. 116. Describe the following with suitable examples:

  1. Double base propellant
  2. Mordant dyes
  3. Broad spectrum antibiotics.

Q. 117.

  1. Explain corrosion of iron as an electro chemical process.
  2. The electrolysis of a metal salt solution was carried out by passing 4 amperesfor 45 minutes. It resulted in the deposition of 2.977g of the metal. If atomicmass of the metal is 106.4g/mole, determine the charge carried by the metal ion.


  1. How does conductivity and molar conductivity of an electrolyte solution vary with the dilution of the solution.
  2. The E0 potentials of two reduction electrodes are Cu+/ Cu = + 0.52V and Cu2+ / Cu+ = + 0.16 V. Calculate the work obtainable from the cell.

Q. 118. (a) Account for the following:

  1. PCl5 solid is ionic in nature.
  2. SF6 is resistant to hydrolysis.
  3. Inter halogen compounds are more reactive than halogens from which it ismade.

(b) Draw the structures of the molecules

  1. P4O10
  2. per oxo mono sulphuric acid.


(a) Account for the following:

  1. PCl5 fumes in air.
  2. Ga is smaller in size than Al.
  3. PbO2 is a good oxidizing agent.

(b) Draw the structures of the molecules

  1. SF4
  2. IF4¯

Q. 119.

  1. what are lipids? Based on their chemical composition, present a classification of lipids.
  2. In reference to DNA molecule what do you under stand by the terms replicationand transcription.


  1. Define the terms (i) codon (ii) native state of protein (iii) Denaturation of protein.
  2. Write the name of the nucleoside which is present only in (i) DNA (ii) RNA.

Q. 120. Define activation energy of a reaction.

Q. 121. A cubic solid is made of two elements X and Y. Atoms Y are at the corners of the cube and X at the body centre. What is the formula of the compound?

Q. 122. State two main functions of carbohydrates in sugarcane.

Q. 123. Why is HF not stored in plain glass bottles?

Q. 124. State one use of acetonitrile.

Q. 125. What values of quantum number, m are permitted for an electron having angular quantum number, 1 = 2 ?

Q. 126. Which types of crystals exhibit piezoelectricity?

Q. 127. What is Tyndall effect?

Q. 128. How many effective sodium ions are located at the centres of faces of a unit cell in a sodium chloride crystal?

Q. 129. Name the first element of 3 d transition metal series.

Q. 130. What are inner transition metals?

Q. 131. State second law of thermodynamics.

Q. 132. Name a direct dye.

Q. 133. Sketch the zwitter ion form of amino acetic acid.

Q. 134. Mention an industrial product manufactured from methanal.

Q. 135. How does a fuel cell operate?

Q. 136. Mention two important uses of methanol.

Q. 137. What is the importance of amino acids to us?

Q. 138. Give an example of associated colloids.

Q. 139. Define order of a reaction.

Q. 140. Zn, Cd and Hg are not considered as transition metals.

Q. 141. Cu,Ag &Au are considered as transition metal though it has 3d,10 configuration.

Q. 142. Zn, Cd and Hg are volatile and Hg is a liquid metal.

Q. 143. Transition metals have high enthalpy of atomisation.

Q. 144. 4d and 5d elements have higher enthalpy of atomisation than 3d elements.

Q. 145. Density of 3d elements increases from Sc to Ni.

Q. 146. Atomic and ionic radii generally decrease along the period.

Q. 147. Zr and Hf have similar size.

Q. 148. Transition metals do not show regular variation of ionisation enthalpies.

Q. 149. 5d elements have higher ionisation enthalpy than 3d and 4d elements.

Q. 150. Generally first ionisation enthalpy increases along the period.

Q. 151. Cr &Cu has higher second ionisation enthalpy (Cr = 24,Cu = 29)

Q. 152. Mn &Zn has higher 3rd ionisation enthalpy (Mn = 25 Zn = 30)

Q. 153. Cu, Ni and Zn normally do not exhibit oxidation state higher than +2.

Q. 154. Transition metals show variable oxidation state.

Q. 155. Transition metals do not show regular variation of E0 values.

Q. 156. E0 Mn3+/Mn2+ have higher +ve value than E0 Cr3+/Cr2+.(Cr=24 Mn=25).

Q. 157. E0 Zn2+/Zn has higher – value. ( Zn = 30).

Q. 158. Transition metals form complexes easily.

Q. 159. Transition metals act as catalysts.

Q. 160. Transition metal compounds are paramagnetic.

Q. 161. Sc3+,Cu+ and Zn2+ are diamagnetic .Sc=21 Cu=29 Zn=30).

Q. 162. Oxidation state of transition metals increases by one unit.

Q. 163. E0 Ni2+/Ni has higher – ve value.

Q. 164. Transition metal compounds are coloured.

Q. 165. Sc3+, Cu+ and Zn2+ are colourless .[Sc = 21 Cu = 29 Zn = 30].

Q. 166. Transition metals form interstitial compounds easily.

Q. 167. Transition metals form alloys easily.

Q. 168. Higher oxides of transition metals are acidic.

Q. 169. Enthalpy of atomization of transition metals reaches a maximum in the middle of each series

Q. 170. Lanthanoid ions are coloured and paramagnetic.

Q. 171. La3+ and Lu3+ are colourless and diamagnetic. (La=57 Lu=71).

Q. 172. Ln are paramagnetic.

Q. 173. La3+ is diamagnetic.

Q. 174. Ce is stable in +4 oxidation state. E0 Ce4+/Ce3+ has higher positive value.

Q. 175. Eu2+ is a good reducing agent.(Eu=63).

Q. 176. Ce4+ is a good oxidising agent .

Q. 177. Yb2+ is stable. It acts as a reducing agent. (Yb=70).

Q. 178. In lanthanoid hydroxide M(OH)3 basic character decreases with increase in atomic number.

Q. 179. Actinoids show greater range of oxidation state than lanthanoids.

Q. 180. Actinoid contraction is greater than lanthanoid contraction.

Q. 181. Ionisation enthalpies of early actinoids are lesser than that of early lanthanoids.

Q. 182. In the d4 species Mn3+ is an oxidising agent where as Cr2+ is a reducing agent

Q. 183. Co(II) is stable in aqueous solution but get oxidised in the presence of complexing agents.

Q. 184. d1 configuration is unstable in transition metals.

Q. 185. Transition metals exhibit higher oxidation state in oxides and flourides.

Q. 186. Zn has lowest enthalpy of atomisation.

Q. 187. First ionization enthalpy of Cr is lower while Zn is higher.(Cr=24, Zn=30)

Q. 188. Zn has lower second ionization enthalpy.

Q. 189. Number of oxidation states at the extreme ends of 3d transition metals are very few.

Q. 190. Transition metals in higher oxidation states are more stabilized in oxides than in fluorides.

Q. 191. E0 Cu2+/Cu is positive.

Q. 192. E0 Sc3+/Sc2+ has lower value (Sc = 21)

Q. 193. E0 Zn3+/Zn2+ have higher positive value.

Q. 194. E0 Fe3+/Fe2+ has comparatively lower positive value than E0 Mn3+/Mn2+ (Mn=25, Fe=26)

Q. 195. E0 V3+/V2+ have negative value (V=23)

Q. 196. Cu2+ (aq) is more stable than Cu+ (aq) despite the d10 configuration of Cu+

Q. 197. Highest fluoride of Mn is MnF4 while highest oxide is Mn2O7.

Q. 198. Oxidising power of Oxides VO2+ <>2O72- <>4-

Q. 199. KMnO4 titration is not carried out using HCl as acid medium.

Q. 200. Third ionization enthalpy of La, Gd and Lu are abnormally low( La = 57, Gd = 64, Lu = 71)

Q. 201. 5f electrons can take part in bonding to a greater extent than 4f electron though both have similar angular wave function.

Q. 202. Highest oxidation state is exhibited by oxoanion in transition metals.

Q. 203. Generally negative value of E0 M2+/M decreases across the series of 3d elements.

Q. 204. It is unsatisfactory to review the chemistry of actinoids in terms of oxidation state.


iCBSE India