Science Class X (CBSE)
Sample Paper Set - III (Solved)

General Instructions :

(i)   All questions are compulsary.
(ii) Question number 1 to 10 are very short answer question,carrying 1 mark each.They are to be answered in one or two sentences.
(iii) Question number 11 to 20 are short answer questions,each carrying 2 marks. Answer to them should not exceed 40 words each.
(iv)  Question numbers 21 to 30 are also short answer questions,each carrying 3 marks. Answer to them should not exceed 60 words each.
(v) Question numbers 31 to 33 are long answer questions,each carrying 5 marks. Answer to them should not normally exceed 100 words each.

Q.1 Name any two semiconductors which are used in the manufacture of solar cells.
Ans1. Silicon and Geruanium.

Q.2 What are "planetesimlas" ?
Ans2. 'Planetesimals' are small objects formed by the condensation of clouds of left over gases surrounding the sun.

Q.3 Name two planets found between the Sun and the Earth.
Ans3. Mercury and Venus.

Q.4 Which has a lower ignition temperature, Kerosene or LPG?
Ans4. LPG.

Q.5 An iron knife kept dipped in a blue copper sulphate turns the blue solution light green. Why?
Ans5. Iron is above copper in the activity series. Thus iron can replace copper from CuSO4 solution. Upon dipping Fe knife in CuSO4 solution, blue CuSO4 gets converted into green FeSO4 and Cu gets separated.

Q.6 Name one metal element and one non-mental element which are obtained on a large scale generally from sea water.
Ans6. Sodium (metal) and Chlorine (non-metal).

Q.7 Which two of the following compounds could belong to the same homologous series? C2H6O2, C2H6O, C2H6, CH4O
Ans7. CH4O and C2H6O belong to the same (CnH2n+1OH) homologous series.


Q.9 Sample of blood of a person, on routine microscopic examination, revealed a high percentage of stippled Red Blood Cells. Name the pollutant responsible for this condition.
Ans9. Lead particles from automotive exhaust.

Q.10 Two lots of cooked dal are maintained at 30° and 45° C respectively. Which one of these two temperatures is likely to cause spoilage earlier?
Ans10. Sample kept at 30°C will get spoilt first because that temperature is more conducive for microbial growth.

Q.11 State two major objectives of the space research programme inour country.
Ans11. Two major objectives identified for the space research programme are:
(i) rapid development of mass communication and education especially in widely dispersed rural communities, and
(ii) timely survey and management of the country's natural resources.

Q.12 "Obtaining of energy from nuclear fusion reactions is preferable to obtaining of energy from nuclear fission reactions". Give tow reasons to justify this statement.
Ans12. Obtaining energy by nuclear fusion would be better because:
(i) the energy liberated in nuclear fusion is very high in comparision to nuclear fission.
(ii) the resulting nuclei are not radioactive and therefore do not pose environmental hazards, in contrast to the nuclear fission reactions.

Q.15 Although hydrogen gas has a very high calorific value still it is not used as an industrial fuel. State four reasons for this.
Ans15. Hydrogen is not used as industrial fuel because:
(i) It burns in air with explosion,
(ii) Its ignition temperature is low and is therefore highly inflammable,
(iii) Its storage and transportation is costly,
(iv) Its production is costly because it is not available free in the atmosphere.

Q.16 Given a solution of substance A, how will you test whether it is saturated or unsaturated with respect to A, at the prevailing temperature? What is observed when a hot saturated solution of a substance is allowed to cool?
Ans16. A saturated solution will not dissolve any more solute into it at the given temperature. To test whether the solution of A is saturated, we will try to dissolve some more of A in the solution. If no more A could be dissolved, the solution of A must be saturated at that temperature. A hot saturated solution when cooled becomes a 'Super-saturated Solution'.


Q.27 "Faulty methods of cooking are responsible for deficiency of nutrition in food." Discuss.
Ans27. Faulty cooking is responsible for deficiency of nutrition in food, because:
(i) deep-frying destroys the nutrients, coagulates proteins, and burns carbohydrates,
(ii) over-cooking of food destroys the useful components of food and burns them,
(iii) washing of cut vegetables and fruits causes loss of water soluble vitamins and nutrients,
(iv) heating of milk substantially destroys the vitamins and coagulates the milk-proteins.

Q.28 Differentiate between biome and biosphere. Why is biosphere considered as a higher level in the organisation?
Ans28. Biome is a big unit, which includes all the ecosystems taken together in a geographical area. For example, in desert biomes or forest biomes one may find a pond, a lake, a grassland and even forest ecosystems
Biosphere is still a bigger unit, which includes all the biomes, world over, taken together as a bigger unit constituting a single large self-sustaining biological system. All the life supporting regions of earth comprise biosphere.
Biosphere is referred to as a system, and is a higher level in the organization because it includes all the ecosystems on earth as well as biomes.

Q.29 What is hybridisation in relation to crops? Describe the process of hybridisation to produce an improved variety of wheat. Mention one advantage and one disadvantage of a high yield variety of wheat.
Ans29. Hybridisation is carrying out of cross breeding of varieties selected to incorporate the desired characters from two or more varieties in a same variety. For hybridisation of wheat It involved:
i) selecting two varieties of crops, which are known to possess at least one of the desired characteristics such as high yield or resistance to diseases;
(ii) cross breeding the varieties;
(iii) selecting the progeny with all the desired characters.
The advantage of HYV is: The yield of the dwarf wheat is substantially high than the traditional varieties
The disadvantage of HYV is: They require better inputs: more water and fertilisers, frequent .weeding and continuous use of pesticides.



Q.32 Described the steps involved in the extraction of aluminium from bauxite using the electrolytic method. Draw a diagram of the electrolytic cell used. Why is some cryolite mixed with purified bauxite in this method?
Ans32. Aluminium is extracted from bauxite, which is primarily Aluminium oxide.Q.33 List two basic steps involved in preservation of food. Describe three common methods used for the preservation of fruits and vegetables. Name any two food preservatives commonly used in our country.

**The basic steps in Food Preservation are:

(a) Elimination of microrganisms responsible for spoilage,
(b) Creation of conditions unsuitable for microbial growth and action.

(b) Creation of conditions unsuitable for microbial growth and action.
(1) Bactericidal Methods: The bacteria are eliminated completely by cooking and canning.
(2) Bacteriostatic Methods: The bacteria and their enzymes are rendered inactive by dehydration,salting, and pickling.

Three commonest methods are:
(1) Dehydration and Sun-Drying: The fruits and vegetables are dried in the sun or by removing their water content under controlled conditions of temperature and humidity. Smoking is a process to dry meat, fish, and their products.

(2) Preservation by Salting and Sugar: Presence of a high concentration of salts ( >15%) or sugars ( >70%) drains out the water from food materials through osmosis and prevents their spoilage by inhibiting bacterial growth. Vinegar, oils, spices and citric acid are also used as preservatives on the same principles.

(3) Chemical Preservation: Two common chemical food preservatives used in our country are:
    (i) Benzoic acid, and
    (ii) Sulphur oxide.
Benzoic acid, or its sodium salt is used to preserve fruits, juices and squash at < 0.1% concentration. SO2 is obtained from sodium metabisulphite by dissolving the latter in the fruit juice, or squash. It is used to preserve colourless fruits and fruity solutions.
Two commonest food preservatves used in our country are:
    (1) Benzoic acid, and
    (2) Sulphur oxide.