Title Science X (Series D3CBA 1) For QR Code.pdf ✅

Shiv Das 2024 (Series: D3CBA/1) SET I Code No. 31/1/1 SECTION-A 1. (b) 2. (c) 3. (c) 4. (c) 5. (d) 6. (c) 7. (d) 8. (b) 9. (c) 10. (a) 11. (c) 12. (c) 13. (d) 14. (a) 15. (c) 16. (d) 17. (a) 18. (b) 19. (c) 20. (c) SECTION-B 21. The chemical reaction between calcium oxide with water is a combination reaction because calcium oxide and water combine to form a single compound calcium hydroxide. CaO + H2O Ca(OH)2 + Heat Quick lime Calcium hydroxide It is also an exothermic reaction because in this reaction a large amount of heat is released. 22. Role of the following in human digestive system: (i) Hydrochloric acid: • Enzyme pepsin is active only in the acidic medium. • It kills any germ which may enter the stomach with food. (ii) Villi: It gives the inner walls of the small intestine a very large surface area. (iii) Anal Sphincter: The exit of faeces is controlled by the anal sphincter. (iv) Lipase: It breaks down the emulsified fats. 23. (a) Difference between Movement of Leaves or Downward Movement of Roots Movement of Leaves Downward Movement of Roots • The folding up of the leaves of sensitive plants on touching is a nastic movement. • The downward movement of the roots is tropic movement. • It is not a directional movement. It means movement is not determined by the direction of stimulus. • It is a directional movement. It means the direction of stimulus determines the direction of movement of the plant. Here the stimulus is gravity and plant root shows positive tropism. • It is growth independent movement. • It is a growth movement. Or (b) • Thyroxine hormone controls the rate of metabolism of carbohydrates, fats and proteins in our body. • Thyroid gland secretes thyroxine hormone. • Iodine is necessary for making thyroxine hormone. Iodised salt can provide all the iodine needed by thyroid gland to make sufficient thyroxine for the body. 24. Given. Object distance, u = –10 cm (Convex mirror) Focal length, f = +15 cm; Position of image, v = ? By using mirror formula, 1 v – 1 u = 1 f ⇒ 1 1 10 1 v 15 ⇒ 1 1 15 1 10 2 3 30 5 30 1 v 6 ⇒ v = +6 cm \ Position of the image is +6 cm and image is formed behind the mirror. 25. (a) When two 6 W resistors are connected in parallel and third resister of 6 W is connected in series combination to this, then equivalent resistance will be 9 W. S-1


Shiv Das S-4 Shivdas Board Exams Question Bank (Science X) 33. (a) Plants Deer Lion If the deer is removed from the food chain, then the number of plants/organisms of first trophic level will increase rapidly as there’s no deer in the food chain to eat it and keep a check. If all the organisms of second trophic level from a forest are removed, then there will not be sufficient food for the third trophic level (lions). Some of the lions will die because of starvation and the population of lions will decrease. No, The decrease in population of lions will disturb other food chains in which lions operate. The hungry lions of the forest can come out of the forest in search of food and may kill domestic animals or human beings. If the lion and deer are operating in other food chains of the food web, the removal of deer population and subsequent reduction in lion population will disturb the balance of ecosystem. Or (b) Gas ‘X’ is Ozone (O3). Ozone is formed in the upper atmosphere by the reaction of ultraviolet (UV) radiations on oxygen (O2) molecules. Importance. The Ozone layer acts as the ozone shield over the surface of the earth and absorbs the harmful ultraviolet radiations of the Sun and prevents them from reaching the earth’s surface. The damaging effect of CFCs (Chlorofluorocarbons) is responsible for the depletion of Ozone layer. Harmful effect. The thinning of Ozone layer results in an increase of UV-B radiation reaching the earth’s surface. This increases the incidence of cataract and skin cancer diminishing the immune system’s function. Measures taken by an international organization to check the depletion of O3 layer. In 1987, in an attempt to protect the Ozone layer, the United Nations Environment Programme (UNEP) forged an agreement among its member countries to freeze CFC production at 1986 levels. It is now mandatory for all the manufacturing companies to make CFC-free refrigerators throughout the world. SECTION D 34. (a) (i) Homologous series. A series of carbon compounds in which the same functional group substitutes for hydrogen on a carbon chain is called a homologous series. There is a difference of —CH2 in the molecular formulae of two nearest compounds of a homologous series. Each such series has same general molecular formula and has a general scientific name. There is a difference of 14 m (unified mass) in the molecular masses of two nearest compounds of a series. (ii) C2H4, C3H6 and C4H8 are the three members of a homologous series Alkenes. The members of a homologous series show a gradual change in their physical properties with increase in molecular mass. As the number of carbon atoms per molecule increases, the melting and boiling points increase. Since C4H8 has more number of carbon atoms than C3H6 and C2H4, thus C4H8 has higher melting and boiling points than C2H4 and C3H6. (iii) All the compounds of a homologous series show similar chemical properties because of the presence of same functional group which decides the properties of the carbon compound regardless the length of the carbon chain. So gradation in chemical properties of homologous series compounds is not required. (iv) • Structure of Aldehyde with molecular form C3H6O: H—C—C—C—H — — — — H H H O H Or Propanal CH3 — CH2 — CHO • Structure of Ketone with molecular form C3H6O: H—C — C — C—H — — — — H H O H H Or CH3 — C — CH3 Propanone O Or (b) (i) Name and structure of ‘X’: H—C—C—OH — — — — H H H H Or Ethanol CH3 — CH2 — OH (ii) When ethanol is heated at 443 K with excess concentrated sulphuric acid, it results in the dehydration of ethanol to give ethene. CH3—CH2—OH Hot conc.  →  H S2 4 O CH2 = CH2 + H2O Ethanol Ethene Water