01 February 2012


Time allowed: 3 hours                                                                                     Maximum Marks:80

  1. Which compounds are responsible for the depletion of ozone layer? 1
  2. Define, 'trophic level'. 1
  3. Give an example of optical phenomena which occur in nature due to atmospheric refraction. 1
  4. Write the electron dot structure of ethene molecule, C 2 H4    1
  5. Explain why the planets do not twinkle but the stars twinkle. 2
  6. Write any two differences between binary fission and multiple fission in a tabular form as observed in cells of organisms. 2
  7. List any four modes of asexual reproductions. 2
  8. List any four characteristics of a good fuel. 2
  9. What are non-renewable resources of energy?  Give two examples of such resources. 2
  10. Answer:
1.      How do you calculate the possible valency of an element from the electronic configuration of its atoms?
2.      Calculate the valency of an element X whose atomic number is 9.  2
  1. The atomic numbers of three elements, X, Y and Z are 9, 11 and 17 respectively.  Which two of these elements will show similar chemical properties?  Why?  2
  2. State the two laws of reflection of light.  2
  3. Draw a ray diagram to show the refraction of light through a triangular glass prism and mark angle of deviation on it.  2
  4. What eye defect is hypermetropia?  Describe with a ra diagram how this defect of vision can be corrected by suign an appropriate lens. 3
  5. Answer:
1.      List two sexually transmitted diseases in each of the following cases: 3
1.      Bacterial infections
2.      Viral infections
2.      How may the spread of such diseases be prevented?
  1. Explain Mendel's view of a dominant trail.  Give an example. 3
  2. Explain the terms: 3
1.      Speciation
2.      Natural selection
  1. Explain how equal genetic contribution of male and female parents is ensured in the progency.3
  2. What is an 'esterification' reaction?  Describe an activity to show esterification. 3
  3. Two elements X and Y belong to group 1 and 2 respectively in the same period of periodic table.  Compare them with respect to: 3
1.      the number of valence electrons in their atoms
2.      their valencies
3.      metallic character
4.      the sizes of their atoms
5.      the formulae of their oxides
6.      the formulae of their chlorides
  1. Draw the ray diagram and also state the position, the relative size and the nature of image formed by a concave mirror when the object is placed at the centre of curvature of the mirror. 3
  2. A ray of light travelling in air enters obliquely into water.  Does the light ray bend towards or away from the normal?  Why?  Draw a ray diagram to show the refraction of light in this situation. 3
  3. Answer:
1.      Draw a diagram of the longitudinal section of a flower and label on it sepal, petal, ovary and stigma.
2.      Write the names of male and female reproductive parts of a flower.                               5
3.      What is fragmentation in organisms?  Name a multicellular organism which reproduces by this method.
4.      What is regeneration in organism?  Describe regeneration in Planaria with the help of a suitable diagram.
  1. Answer:
1.      In a tabular form, differentiate between ethanol and ethanoic acid under the following heads: 5
1.      Physical state
2.      Taste
3.      NaHCO3 test
4.      Ester test
2.      Write a chemical reaction to show the dehydration of ethanol.
3.      What is a soap?  Why are soaps not suitable for washing clothes when the water is hard?
4.      Explain the action of soap in removing an oily spot from a piece of cloth.
  1. Anaswer:                     5
1.      If the image formed by a lens is diminished in size and erect, for all positions of the object, what type of lens is it?
2.      Name the point on the lens through which a ray of light passes undeviated.
3.      An object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm.  The distance of the object from the lens is 30 cm.  Find (I) the position (ii) the magnification and (iii) the nature of the image formed.
4.      One half of a convex lens is covered with a black paper.  Will such a lens produce an image of the complete object?  Support your answer with a ray diagram.
5.      An object 5 cm high is held 25 cm away from a converging lens of focal length 10 cm.
1.      Draw the ray diagram and
2.      Calculate the position and size of the image formed.
3.      What is the nature of the image.

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