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CBSE class XII Chemistry Important Questions


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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CBSE Important Questions Physics Electrostatics Class XII


Important Questions
Class XII
Physics : Electrostatics

Questions having one mark each:
  1. Write the S.I unit of
    i. electric field intensity
    ii. Electric dipole moment.
  2. How does the coulomb force between two point charges depend upon the dielectric constant of the intervening medium?
  3. Draw an equipotential surface for a system, consisting of two charges Q, -Q separated by a distance ‘r’ apart.
  4. Show graphically the variation of charge ‘q’ with time’t’ when a condenser is charged.
  5. What orientation of an electric dipole in a uniform electric field would correspond to stable equilibrium?

Questions having 2 marks each:
  1. Two point charges, q1 =10×10-8 C and q2 = -2×10-8 C are separated by a distance of 60 cm in air.
    i. Find at what distance from the 1st charge, q1, would the electric potential be zero.
    ii. Also calculate the electrostatic potential energy of the system.
  2. Two capacitors of capacitance 6µF and 12µF are connected in series with a battery. The voltage across the 6µF capacitor is 2V. Compute the total battery voltage.
  3. An electric dipole is free to move in a uniform electric field. Explain its motion when it is placed
    i. parallel to the field,
    ii. perpendicular to the field.
  4. An electric dipole of length 10 cm having charges ± 6×10-3 C, placed at 300 with respect to a uniform electric field experiences a torque of 6√3 N-m. Calculate
    i. magnitude of electric field
    ii. the potential energy of the dipole.
  5. Electric charge is distributed uniformly on the surface of a spherical rubber balloon. Show how the value of electric intensity and potential vary
    i. on the surface
    ii. inside and
    iii. outside?

Questions having 3 mark each:
  1. State Gauss’s theorem in electrostatics. Apply this theorem to derive an expression for electric field intensity at a point near an infinitely long straight charged wire.
  2. Explain the underlying principle of working of a parallel plate capacitor.
    If two similar plates, each of area A having surface charge densities +σ and –σ are separated by a distance‘d’ in air, write the expressions for
    i. The electric field at points between the two plates.
    ii. The potential difference between the plates.
    iii. The capacitance of the capacitor so formed.
  3. A 20 µF capacitor is charged by a 30 V d.c. supply and then connected across an uncharged 50 µF capacitor. Calculate
    i. the final potential difference across the combination.
    ii. Initial and final energies. How will you account for the difference in energies?
  4. The battery remains connected to a parallel plate capacitor and a dielectric slab is inserted between the plates. What will be the effect on its
    i. capacity
    ii. charge
    iii. potential difference
    iv. electric field
    v. energy stored?
  5. Define the term electric potential due to a point charge. Calculate the electric potential at the centre of a square of side √2 m, having charges 100 µC, -50µC, and 20µC and-60µC at the four corners of a square.

Questions having 5 marks each:
  1. Explain the principle on which Van-de-Graaff generator operates. Draw a labeled schematic sketch and write briefly its working. A Van-de- Graaff type generator is capable of building up potential difference of 15×106 V. The dielectric strength of the gas surrounding the electrode is 5×107 Vm-1. What is the minimum radius of the spherical shell required?
  2. An electric dipole is held in a uniform electric field.
    i. Show that no translatory force acts on it.
    ii. Derive an expression for the torque acting on it.
    iii. The dipole is aligned parallel to the field. Calculate the work done in rotating it through 1800
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CBSE class XII Physics Optical instruments


Q. 1. A telescope has an objective of focal length 50 cm and eyepiece of focal length 5 cm .The least distance of distinct vision is 25cm.The telescope is focused for distinct vision on a scale 200 cm away from the object. Calculate (a) the separation between the objective and eyepiece and (b) the magnification produced. (70.83 cm, -2)
Q. 2. A telescope objective of focal length 1 m forms a real image of the moon 0.92 cm in diameter. Calculate the diameter of the moon taking its mean distance from the earth to be 38x104 km. (3.5 x106 m)
Q. 3. An angular magnification of 30X is desired using an objective of focal length 1.25 cm and an eyepiece of focal length 5 cm. How will you set up the compound microscope? (L=11.67cm.)
Q. 4. A compound microscope is used to enlarge an object kept at a distance of 0.30 m from its objective, which consists of several convex lenses and has focal length 0.02 m. If a lens of focal length 0.1 m is removed from the objective, find out the distance by which the eyepiece of the microscope must be moved to refocus the image? (9cm.)
Q. 5. An amateur astronomer wishes to estimate roughly the size of the sun using his crude telescope consisting of an objective lens of focal length 200 cm and eyepiece of focal length 10 cm. By adjusting the distance of the eyepiece from the objective, he obtains an image of the sun on a screen 40 cm. behind the eyepiece. The diameter of the sun’s image is measured to be 6 cm. What is his estimate of the sun’s size, given that average earth – sun distance is 1.5x1011 m. (1.5 x 109 m)
Q. 6. A 35 mm slide with a 24 mm x 36 mm picture is projected on a screen placed 12 m from the slide. The image of the slide picture on the screen measures1.0mx1.5 m. Determine the location of the projection lens and its focal length? (28.1cm, 27.5 cm)
Q. 7. An eyepiece of a telescope consists of two plano convex lenses L1 and L2 each of focal length f separated by a distance of 2ƒ/3. Where should L1 be placed relative to focus of the objective lens of telescope, so that the final image through L2 is seen at infinity? (ƒ/4)
Q. 8. A telescope has a objective of diameter 60 cm. The focal lengths of the objective and eyepiece are 2 m and 1.0 cm respectively. The telescope is directed to view two distant point sources of light (e.g. two stars of a binary). The sources are roughly at the same distance ( 104 light years) along the line of sight, but separated transverse to the line of sight by a distance of 1010 m. Will the telescope resolve the two objects? (Take, λ =6x10-7 m for mean yellow color.) (No)
Q. 9. The separation between the eyepiece (of focal length 0.3 m) and objective (of focal length 0.4 m) of a microscope is 0.2 m. The eyepiece and the objective are to be interchanged such that the angular magnification of the instrument remains the same. What is the new separation between the lenses? Hint: use, m = (0.3m)
Q. 10. The image of the moon is focused by a converging lens of focal length 50 cm on a plane screen. The image is seen by an unaided eye from a distance of 25 cm. Find the angular magnification achieved due to the converging lens? (- 2)
Q. 11. The objective of telescope A has a diameter 3 times that of the objective of telescope B. How much greater amount of light is gathered by A compared to B? Show that range of A is three times the range of B? [Hint: Intensity α ] (9 times)
Q. 12. The diameter of sun is several hundred times bigger than the moon, still at the time of solar eclipse, the moon covers the entire sun. How?
Q. 13. How does magnifying power change with change in length of tube of a given telescope and microscope each?
Q. 14. Distinguish between linear magnification and angular magnification. When are these two magnifications equal? 15. When viewing through a compound microscope, our eye should be positioned not on the eyepiece, but a short distance away from it. Why? How much should be that short distance between the eye and the eyepiece?
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CBSE Sample Papers 2012


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Sample Question Papers and Marking Scheme for Board Exams 2012. All Sample Papers for Class 9th, 10th and 12th are as per latest syllabus of CBSE.
Class IX and X Class XII
All India Secondary School Examination (AISSE) in the 10th standard and All India Senior School Certificate Examination (AISSCE) in the 12th are the two exams conducted by the CBSE board. Now that we have brief idea about CBSE, let us understand how it works and what the advantages of this board are:
  • Language of Instruction for CBSE curriculum is available both in English as well as Hindi.
  • CBSE is a recognized board by the Government of India. The syllabus of CBSE is set with an idea of providing objective knowledge which is tested in the competitive examinations.
  • CBSE has a student oriented syllabus that is developed understanding the needs and requirements of an individual child.
  • CBSE with the introduction of its new concept of Grading System has really helped the children who are not able to get qualifying marks in the Board Examination.
CBSE is driving towards enhanced learning solutions.
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CLASS IX BIOLOGY MCQs-BASED ON PRACTICALS

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