CBSE Set Qa2 Science Class X 1998 Sample Test Papers For Class 10th for students online

Science Class X (CBSE)
You are on answers 21 to 33

Q21. Describe the construction of a solar cooker. How does it cause a rise in temperature to cook food?
Ans21. A solar heater consists of a box made of an insulator material. Into this outer box is placed an inner box made of a metal.The inner walls of the metallic box are painted black.The space between the outer box and the inner-box is filled with some insulating material. A glass sheet is put on the box which can be opened or closed as a lid. A mirror reflector is fixed at the back of the solar cooker.The food material to be cooked is put in the metallic vessels which are then placed inside the solar cooker box.


When the sun rays fall on the box, the black inner surface of the solar cooker absorbs the solar heat energy and becomes hot. This heat cooks the food material kept in the container.The black surface, the insulator material, the glass sheet and the mirror maximise the heat absorption, heat retention, and minimise the heat loss.

Q22. What are rocket propellants? Mention any two of their important characteristics. Give an example of liquid propellants.
Ans22. Rocket Propellant: The special fuels that are highly compact and burn rapidly and completely are called rocket propellant. These are used to create a massive jet of backward streaming gases to propell the rockets forward. They must have the following characteristics:
(i) They must be capable of producing a very large volume of gases for every gram of fuel burnt, (ii) The combustion must proceed at an exceptionally fast rate,
(iii) The fuels must burn completely leaving no dead weight of residue.
An example of the liquid propellant is a mixture of methyl hydrazine and the oxidiser dinitrogen teraoxide.

4CH₃NHNH₂ + 5N₂O₄ 4CO₂ + 9N₂ + 12H₂O

Q23. Name the process involved in the liberation of energy in (i) the sun and (ii) a nuclear reactor.Mention any two differences between the two processes.
Ans23.(i) Process involved in liberation of energy in sun : Nuclear fusion
(ii) Process involved in liberation of energy in a nuclear reactor : Nuclear Fission

Q24. The mass of a star A is one tenth that of star B. If the mass of A is nearly equal to that of the sun, which one of the two stars will end up as supernova? What would happen to the other star at the end of red giant phase?
Ans24. Mass of A is nearly equal to that of sun. B has mass ten times that of A that is ten times that of the, Sun. Therefore, the star B is will end up as supernova.
The star A will end up as a White Dwarf Star.
The star A after entering the red giant stage will lose its expanding outershell.The core of red giant star left behind would gradually condense into an exremely dense ball of matter. Due to contraction of condensation, high temperature would be produced in the core. At this high temperature Helium present in the core would fuse to form higher elements like carbon and
liberate a lot of energy. The energy liberated by these fusion reactions cause the small core glow until helium lasts into it. This is how the white dwarf star would be formed from A.

Q25. Define isomerism. Write the structural formulae and the names of the isomers of butane.
Ans25. Isomerism is the phenomenon of occurrence of compounds of same molecular formulae but different structural arrangements of atoms in them. The different compounds representing this phenomenon are Isomers for each other.

n-butane iso-butane

Q26. Describe any three ways in which the water is important for the activities of living beings.
Ans26. Water is important for living beings:
As solvent: water is almost a universal solvent. Many things which the living animals have to ingest and need to take into their cell as metabolite have to be dissolved and water is the best solvent and carrier for such things.
As habitat of organisms: Aquatic organisms need water as a medium for living. Water was the medium where life originated first.
As temperature regulating agent: Water serves as a temperature regulating agent in a way that it spreads temperature uniformly among colder and warmer zones. It cools body by sweating and evaporation.

Q27. A cow is being fed on straw, oil cake, oilseeds, gram and bajra. To what classes of cattle feed do these items belong and what is their importance?
Ans27. Straw belongs to the class Roughage.
Oil-cake, oil-seeds, gram, and bajra belong to the class Concentrate.
Concntrates provide rich nutrition in one or the other nutrient. Roughage provide the fibres, and coarse low nutrients. Roughage also makes the bulk of the feed.

Q28. Moisture content of four food items P, Q, R and S is 10%, 15%, 25% and 50% respectively. Which of these require cold storage and which ones dry storage? Give reasons.
Ans28. A drier article with less moisture content can be "Stored Dry" whereas a watery article with more moisture content need be "Stored Cold".
Among P, Q, R, and S; P and Q have moderate moisture content (10% and 15% respectively) and therefore are suitable for Dry Storage, whereas R and S have high moisture content (25% and 50%) and therefore need Cold Storage.

Q29. Name the radiations absorbed by the ozone layer. Give any two causes of the depltetion of ozone layer. Name the disease likely to be caused due to its depletion.
Ans29. Ultraviolet radiation is absorbed by the ozone layer.
Causes of the depletion of ozone layer :
(1) the emmissions produced by the supersonic jets
(2) fluorocarbons and chloroflourocarbons, used in aerosol sprayers and refrigeration. The diseases likely to be caused due to depletion of ozone layer are skin cancer and severe sun-burns.

Q30. What is nitrogen fixation? Mention two points of difference between nitrification and denitrification processes. Name the organism involved in these processes.
Ans30. Nitrogen fixation is the process of converting molecular form of N₂ to a usable form, i.e. nitrates. Nitrogen fixation is achieved (1) Biologically: symbiotically as well as asybiotically; and
(2) Chemically: atmospherically as well as industrially.

Q31. Draw diagram of a nuclear reactor. What is the role of moderators in it? How are nuclear reactors used to generate electricity?
Ans31. Nuclear reactors were discovered by Enrico Fermi. The nuclear reactor in which heavy water is used as moderator, is known as swimming pole atomic reactor. While the nuclear reactor in which graphite is used as moderator is known as atomic pile.

Role of moderator is to slow down the fast moving secondary neutrons produced during the fission. They prevent the rate of chain reaction to be uncontrollably fast. Suitable materials to be used as moderator are heavy water,graphite, cadmium, or boron.

Working of Nuclear Power Plant:
The fuel rods made of enriched U-235 are put in the core and the reactor core is sealed. The control rods are completely inserted inside the graphite core of the reactor. The cadmium rods are initially put fully inside the graphite core so that they may absorb all the neutrons being emitted by U-235 and prevent the fission chain reaction from starting at once. The control rods are then gradually withdrawn from the reactor core till they have corrected the
number of neutrons required for a controlled fission reaction to take place.
Once the nuclear fission of U-235 begins, the fission-energy is released.
The intense heat generated in the reactor is withdrawn by ciruclating liquid sodium through pipes embedded in the reactor. The molten hot sodium is circulated in the coils of heat exchangers where it heats water to produce steam. This superheated high pressure steam formed in the heat exchanger is passed into the turbine chamber to rotate the steam turbine. The roatation of the steam turbine moves the electricity generator and produces electricity.



Q32. (I) Describe the steps involved in manufacture of blistor coppor from concentrated copper sulphide ore.
(ii) State the process of obtaining pure coper from blister copper with the help of a labelled diagram.
(iii) Name the elements which are mixed with copper to prepare German silver.

Ans32. (i) Extraction of copper:
Copper is normally extracted from its sulphide ores, CuS which has rocky impurities into it.
(1)The dressing of the ore: The dressing is done by froth floatation method. The froth containing CuS are scooped off and roasted.
(2)Roasting: By roasting most of CuS is converted into CuO:

(3)Reduction: After some time the air supply is stopped. In the absence of the air supply the following reaction occurs in the furnace:

Copper thus formed is in the molten state. Since, sulphur dioxide gas passes through molten copper, sort of blisters are developed on the surface of copper, which is known as blister copper.
(4)Electrorefining: Blister copper is refined by electrolysis process. The impure metal is used as anode and a strip of pure metal is used as cathode. The solution of CuSO₄ is used as electrolyte. On passing the current pure metal gets depositted on the cathode and the anode is used up.
The impurities of less reactive metal such as iron etc. remain in the solution, whereas less reactive metal impurities such as gold etc. sink at the bottom.



(ii) German silver is an alloy of copper, nickel and zinc.

Q33.(i) Name the elements that constitute proteins.
(ii) What are the end products of protien digestion and where are they absorbed.
(iii) Name any three types of protiens found in our body and mention thier functions.
Ans33(i) Carbon (C), Hydrogen (H), Oxygen (O), Nitrogen (N) and Sulphur (S) constitute proteins
(ii) Proteins are broken into their constituent amino acids by the end of digestion. The digestion of proteins occurs in the small intestine, and the amino acids produced in the process are absorbed from the intestine.
(iii)