Class  X^th Science
Previous Year Question Papers (Delhi)

Section - A

1. Draw a figure to show how the rate of a chemical reaction in general changes as the temperature of reactants is increased step-wise. 1


2. Name the classes of organic compounds represented by the following formulae :


3. Name any two neutral oxides. 1


4. What type of force or forces keep the Sun and its planets in their respective places ?


OR

What force makes an apple on a tree to fall to the ground and what force makes a balloon filled with
hydrogen to rise into air ? 1


5. How can it be shown that a magnetic field exists around a wire through which a direct electric current is passing ? 1


6. What is the chemical name of washing soda ? Name the three chief raw materials used for making washing soda by the Solvay process. 2


7. What is meant by ‘fermentation’ ? Write chemical equations for the two steps involved in preparing ethanol by the fermentation of molasses.


OR

Name the main products formed when :
(i) Ethanol is oxidised by an alkaline solution of KMnO4.
(ii) Propanone and hydrogen cyanide form an addition compound.
(iii) Sodium ethanoate is heated with soda lime.
(iv) Methanal is reduced with hydrogen in the presence of finely divided palladium. 2


8. To which galaxy does our earth belong ? How is the shape of this galaxy described ?
‘Our universe is expanding’. What does it mean ? 2


9. In cases of artificial satellites what are ‘equatorial’ and ‘polar’ orbits ? Which type of these satellite orbitals will be suitable for collecting data for weather prediction and why ? 2


10. Which type of nuclear process is currently used in nuclear electricity generators ? Give one example each for the substances used in this context as :
(i) coolants, 
(ii) moderators, and 
(iii) nuclear fuel. 2


11. When will the reversible reaction,
N2(g) + O2(g)=2NO(g)
be said to be in equilibrium state ? Write the formula co-relating the concentration of involved substances in this equilibrium state. A reversible reaction has a very low value of its equilibrium constant. What does it signify for the rate of progress of the reaction ? 3


12. Besides being large molecules what is the other essential similar structural character of all polymers ? Give one example each for the formation of (0 an addition polymer and (if) a condensation polymer.

OR 

State the monomers used and one use each for :
(a) Neoprene, 
(b) Teflon and 
(c) Natural rubber. 3


13. (a) What are strategic metals ? Give one example also.
(b) State the reason for the following behaviour of zinc metal :
On placing a piece of zinc metal in a solution of mercuric chloride it acquires a shining silvery surface but when it is placed in a solution of magnesium sulphate no change is observed. 3


14. Write chemical equations for the reactions taking place when :
(i) A piece of calcium metal is placed in water. (ii) Ammonia gas comes in contact with hydrogen chloride gas. (iii) Sulphur is heated with concentrated H2SO4. 3


15. State the formula correlating the electric current flowing in a conductor and the voltage applied across it. Also show this relationship by drawing a diagram. What would be resistance of a conductor if the current flowing through it is 0.35 ampere when the Xpotential difference across it 1.4 volt ? 3


16. The radius of curvature of a convex mirror used on a moving automobile is 2.0 m. A truck is coming behind it at a constant distance of 3.5 m. Calculate (i) the position, and (ii) the size of image relative to the size of the truck. What will be the nature of the image ? 3


17. (a) Draw a ray diagram to show passage of two rays of light through a rectangular slab of glass, when the angle of incidence is zero in one case and a little less than 90° in the other case. (b) Prove that if a ray enters a rectangular glass slab obliquely and emerges from the opposite face, the emergent ray will be parallel to the incident ray.


OR

(a) State Snell’s law of refraction of light.
(b) A transparent medium A floats on another transparent medium B. When a ray of light travels obliquely from A into B the reflected ray bends away from the normal. Which of the media A and B is optically denser and why ? 3


18. Name an important ore of aluminium. What are the impurities associated with it? How is pure aluminium obtained from this ore ? Draw a labelled diagram of the plant.


OR

(a) What method for concentration of ore is preferred in each of the following cases and why ?
(i) The ore has higher density particles interspersed with a large bulk of low density impurities. (ii) The ore consists of copper sulphide intermixed with clay particles.
(b) Give an example of amalgams. 5


19. (a) With the help of a labelled ray diagram show how the image is formed in an astronomical telescope in normal adjustment. Write formulae for
(i) calculating the magnification by the telescope. (ii) finding the length of the tube required for the telescope.
(b) The objective of an astronomical telescope has a focal length of 2.0 m and its eyepiece has a focal length of 0.5 cm. When the telescope is in normal adjustment, find
(i) magnification by the telescope. (ii) the length of the telescope. 5


20. Name any three forms of energy of the oceans which can be converted into usable energy forms. Describe how it is done in each case. What is the likelihood of their use on a large scale ?


OR

What are (i) solar concentrators and (ii) solar cell panels ? How are they an improvement on simple devices ? Why is it that solar cell panels are costly ? 5



Section - B

21. State one point of difference between metacentric chromosomes and telocentric chromosomes. 1


22. Which hormone is responsible for the development of moustache and beard in men ? 1


23. In terms of evolution, what is the significance of homology between a human hand and awing of a bird ? 2


24. Draw a labelled diagram of the human urinary system. 2


25. How can air pollution lead to :
(i) skin cancer in man ? (ii) melting of ice cap of earth ? 2


26. What is the difference between sensory and motor neutrons ? Which parts of human brain are responsible for auditory reception and sensation of smell ?


OR

What is the importance of the following processes occurring during photosynthesis in plants ? (i) Emission of electrons from chlorophyll. (ii) Photolysis of water. 3


27. Name any two sexually transmitted diseases (STDs). How do these infectious diseases spread from one person to another ? Give two symptoms of STDs. 3


28. (i) What does the abbreviation UASB stand for ?
(ii) Explain the process of sewage treatment after it has passed through UASB. 3


29. Distinguish between aerobic and anaerobic respiration in terms of end-products and energy released. Why do smokers develop an over strained heart ? 3


30. (i) State two structural differences between an artery and a vein.
(ii) Name a non nucleated cell present in human blood and state one function of this ceil.
(iii) Draw a labelled diagram of human heart. 5