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QUESTIONS FROM CBSE EXAMINATION PAPERS
I. VERY SHORT ANSWER QUESTIONS (1 Mark)
1. Why do silver ornaments loose their shine when kept for some time? [2010 (T-1)]
2. Name a metal other than aluminium that is covered with an oxide film layer. [2010 (T-1)]
3. Name one metal and one non-metal which exist in liquid state at room temperature? [2010 (T-1)]
4. Name a non-metal which is lustrous and a metal which is non-lustrous. [2010 (T-1)]
5. Name two metals which have very low melting point. [2010 (T-1)]
6. If copper metal is heated over a flame, it develops a coating. What is the colour and composition of this coating? [2010 (T-1)]
7. Why is sodium metal kept immersed in kerosene oil? [2010 (T-1)]
8. Name one metal which react with very dilute HNO3 to evolvehydrogen gas. [2010 (T-1)]
9. A non-metal X exists in two different forms Y and Z. Y is the hardest natural substance, whereas Z is a good conductor of electricity. Identify X, Y, and Z. [2010 (T-1)]
10. An element A forms two oxides AO and AO2. The oxide AO is neutral whereas the oxide AO2 is acidic in nature. Would you call element A a metal or non-metal. [2010 (T-1)]
II. SHORT ANSWER QUESTIONS (2/3 Marks)
11. What are the constituents of solder alloy? Which property of solder makes it suitable for weldingelectricalwires? [HOTS]
12. What happen when (a) ZnCO3 is heated in the absence of oxygen? (b) a mixture of Cu2O and Cu2S is heated?[HOTS]
13. A metal P is placed in an aqueous solution of Q. In a few hours metal Q was deposited on metal P. Which metal amongst P and Q is more reactive and why? [HOTS]
14. State reasons for the following observations:
(i) The shining surface of some metals becomes dull when exposed to air for a long time.
(ii) Metals sulphides occur mainly in rocks but metal halides occur mostly in sea and lake. 
15. Differentiate between roasting and calcinations processes used in metallurgy. Give an exampleof each. 
16. Give reason for the following:
(a)Gold and silverare used to make jewellery.
(b) Carbonate and sulphide ores are usually converted into oxides prior to reduction during the process of extraction. 
17. Compound X and aluminium are used to join railway tracks. [HOTS]
(a) Identity the compound X (b) Name the reaction (c) Write down its reaction.
18. Give the steps involved in the extraction of metals of low and medium reactivity from their respective sulphide ores. [HOTS]
19. (a) What type of reaction is to be performed to ascertain and verify the position of metals in the reactivity series?
(b) If an iron nail immersed in the aqueous solution of copper sulphate, what are the changes happening to the nail and to the solution?
(c) Write the balanced chemical equation for the reaction between iron metal and aqueous copper sulphate solution. [2010 (T-1)]
20. Name two metals which react violently with cold water. Write any three observations you would make when such a metal is dropped into water. How would you identify the gas evolved, if any, during the reaction? 
Question 1 ( 1.0 marks)
Name the part of our eyes that helps us to focus near and distant objects in quick succession.
The part of our eyes that helps us to focus near and distant objects in quick succession is eye lens.
Question 2 ( 1.0 marks)
The outer surface of a hollow sphere of aluminium of radius 50 cm is to be used as a mirror. What will be the focal length of this mirror? Which type of spherical mirror will it provide?
The focal length of the mirror will be
The outer surface of a hollow sphere of aluminium will act as a convex mirror.
Question 3 ( 1.0 marks)
What is nature of the image formed by a concave mirror if the magnification produced by the mirror is + 4?
The nature of the image formed by a concave mirror if its magnification is +4, will be virtual, erect and larger than the object.
Question 4 ( 1.0 marks)
A charged particle enters at right angles into a uniform magnetic field as shown. What should be the nature of charge on the particle if it begins to move in a direction pointing vertically out of the page due to its interaction with the magnetic field?
The nature of charge on the particle should be positive.
Question 5 ( 1.0 marks)
On what basis is a chemical equation balanced?
Law of conservation of mass forms the basis of balancing chemical equations. In a balanced chemical equation, the number of atoms of each element is equal on both sides of the equation.
Question 6 ( 1.0 marks)
State two characteristic features of carbon which when put together give rise to a large number of carbon compounds.
The two characteristic features of carbon which when put together give rise to large number of carbon compounds are—
1. The ability to catenate
2. Tetravalency of carbon atom
Question 7 ( 2.0 marks)
Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.
A chemical change can be confirmed by any of the following observations:
ï½ï½ï½ï½ Change in temperature
ï½ï½ï½ï½ Evolution of gas
For example: Calcium oxide reacts vigorously with water to produce calcium hydroxide. During this process, a large amount of heat is also evolved, which increases the temperature of the system. This confirms that a chemical reaction has taken place.
Also, when calcium carbonate is heated, it decomposes to form calcium oxide and carbon dioxide.
In this reaction, calcium carbonate breaks down to form calcium oxide and carbon dioxide. Here, evolution of the gas (carbon dioxide) confirms that a chemical reaction has taken place.
Question 8 ( 2.0 marks)
What are fossil fuels? Write two disadvantages of burning fossil fuels.
Fossil fuels are those fuels that were formed by remains of dead animals and plants that got buried deep inside the earth millions of years ago. Fossil fuels mainly contain hydrocarbons. Coal, petroleum and natural gas are fossil fuels.
Disadvantages of burning fossil fuels:
1. The burning of fossil fuels produces large amounts of acidic gases such as sulphur dioxide and nitrogen dioxide. These acidic gases combine with rainwater to form acids such as sulphuric acid and nitric acid. Acid rains have been observed in many parts of the world after the industrial revolution in Europe.
2. Fossil fuels such as coal leave a lot of ash content after burning. This ash is mostly thrown into rivers, leading to their pollution. Such contaminated water causes serious health problems.
3. The burning of fossil fuels produces smoke, leading to air pollution.
4. The burning of fossil fuels releases carbon dioxide a greenhouse gas which is the main cause for global warming.
5. Fossil fuels have a limited supply on the earth. They cannot be replenished at the same rate at which they are used.
(Any two points will serve the purpose)
Question 9 ( 2.0 marks)
Two coils A and B of insulated wires are kept close to each other. Coil A is connected to a galvanometer while coil B is connected to a battery through a key. What would happen if
(i) a current is passed through coil B by plugging the key, and
(ii) the current is stopped by removing the plug from the key?
Explain your answer mentioning the name of the phenomena involved.
(i) When current is made to pass through coil B, by plugging the key in, for that instant, the galvanometer connected to coil A shows a deflection, i.e., current passes through coil A as well.
(ii) When current is stopped through coil B by taking the plug of the key out, for that instant, the galvanometer connected to coil A again shows a deflection, this time, however, in the opposite direction. That is, a current passes through coil A in the opposite direction.
The observations are made because whenever we change the current in the coil B, the magnetic field associated with it and the coil A in its proximity changes. At the very instant of plugging the key in or taking the plug out, there is an instantaneous flow of current and a change in the magnetic field associated with the coil B. During this instantaneous moment, the current in coil B reaches from zero to the maximum or from the maximum to zero. This changing magnetic field of coil B induces a current in the coil A.
The phenomenon is known as electromagnetic induction.
Question 10 ( 2.0 marks)
What is a solenoid? Draw the pattern of magnetic field lines of a solenoid through which a steady current flows. What does the pattern of field lines inside the solenoid indicate?
A solenoid is a coil of several circular turns of insulated conducting wire, wrapped closely in the shape of a cylinder.
Pattern of magnetic field lines of a solenoid through which a steady current flows:
The pattern of magnetic field lines inside a current-carrying solenoid indicates that the magnetic field is uniform, i.e., strength of the magnetic field is the same, everywhere inside the solenoid.
Question 11 ( 2.0 marks)
What is Hypermetropia (far sightedness)? Draw a ray diagram to show how this defect can be corrected using a lens.
Hypermetropiais a defect of vision in which a person cannot see nearby objects clearly, but has no problems in seeing distant objects.
Corrected vision for a hypermetropic eye by using a convex lens:
Question 12 ( 2.0 marks)
Mention any four limitations in harnessing wind energy on a large scale.
Four limitations in harnessing wind energy on a large scale are as follows:
i) Wind mills or wind energy plants can only be built in places where wind blows at a high speed for the greater part of a year.
ii) For a large-scale windmill to be productive, the wind speed must be atleast 15 km/h.
iii) A large-scale windmill establishment requires large area of land.
iv) The initial cost of establishment of the farm is quite high.
Question 13 ( 3.0 marks)
At what distance should an object be placed from a lens of focal length 25 cm to obtain its image on a screen placed on the other side at a distance of 50 cm from the lens? What will be the magnification produced in this case?
Focal length, f = 25 cm
Image distance, v = 50 cm
Form the lens formula,
Or, u = 50 cm
The object must be placed 50 cm away from the lens, on the other side to produce a magnification of 1.
Question 14 ( 3.0 marks)
Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electronic shells but different number of electrons in their outermost shell. It was found that elements A and G combine to form an ionic compound. This compound is added in a small amount to almost all vegetable dishes during cooking. Oxides of elements A and B are basic in nature while those of E and F are acidic. The oxide of D is almost neutral. Based on the above information answer the following questions:
(i) To which group or period of the periodic table do the listed elements belong?
(ii) What would be the nature of compound formed by a combination of elements B and F?
(iii) Which two of these elements could definitely be metals?
(iv) Which one of the eight elements is most likely to be found in gaseous state at room temperature?
(v) If the number of electrons in the outermost shell of elements C and G be 3 and 7 respectively, write the formula of the compound formed by the combination of C and G.
(i) The elements A, B, C, D, E, F, G and H belong to the third period of the periodic table and to the following groups.
A belongs to group 1
B belongs to group 2
C belongs to group 3
D belongs to group 14
E belongs to group 15
F belongs to group 16
G belongs to group 17
H belongs to group 18
(ii) The compounds formed by B and F would be ionic in nature.
(iii) Elements A and B are definitely metals.
(iv) Element H is most likely to found in gaseous state at room temperature.
(v) The formula of the compound will be CG3.
Question 15 ( 3.0 marks)
No chemical reaction takes place when granules of a solid, A, are mixed with the powder of another solid, B. However when the mixture is heated, a reaction takes place between its components. One of the products, C, is a metal and settles down in the molten state while the other product, D, floats over it. It was observed that the reaction is highly exothermic.
(i) Based on the given information make an assumption about A and B and write a chemical equation for the chemical reaction indicating the conditions of reaction, physical state of reactants and products and thermal status of reaction.
(ii) Mention any two types of reactions under which above chemical reaction can be classified.
(i) Solid A is assumed to be MnO2and solid B to be Aluminium (Al).
When the mixture of MnO2andAl is heated, manganese (Mn) is produced in molten state and aluminium oxide (Al2O3) floats over it. Mn is produced in the molten state as a lot of heat energy is released in the process.
The chemical equation for the reaction can be written as:
(ii) The types of reaction under which the above reaction is classified are—
1. Redox reaction
2. Displacement reaction
Question 16 ( 3.0 marks)
Name the functional group of organic compounds that can be hydrogenated. With the help of suitable example explain the process of hydrogenation mentioning the conditions of the reaction and any one change in physical property with the formation of the product. Name any one natural source of organic compounds that are hydrogenated.
The functional group of organic compounds that can be hydrogenated are alkenes and alkynes
Hydrogen can be added to unsaturated hydrocarbons in the presence of nickel to yield saturated hydrocarbons. In this reaction, nickel acts as a catalyst.
Onhydrogenation, the unsaturated fatty acids which are liquid at room temperature become saturated and change to solid.
A natural source of organic compound that is hydrogenated is vegetable oil.
Question 17 ( 5.0 marks)
Derive the expression for the heat produced due to a current I flowing for a time interval t through a resistor R having a potential difference V across its ends. With which name is the relation known? How much heat will an instrument of 12W produce in one minute if it is connected to a battery of 12V?
Explain with the help of a labelled circuit diagram how you will find the resistance of a combination of three resistors, or resistance R1, R2and R3, joined in parallel. Also mention how you will connect the ammeter and the voltmeter in the circuit when measuring the current in the circuit and the potential difference across one of the three resistors of the combination.
Consider a resistor of resistance R. Let the current flowing through this resistor be I and the potential difference across it be V.
In time t, let Q amount of charge flows through the resistor.
Work done on moving this charge, W = VQ ... (1)
According to the definition of electric current,
Q = I ï½ï½ï½ï½ t
Putting this in equation (1),
W = V ï½ï½ï½ï½ I ï½ï½ï½ï½ t
This work done is dissipated as heat.
Heat produced, H = W = VIt
H = VIt ... (2)
According to Ohms law, V = IR.
Putting this in equation (2),
H = IR ï½ï½ï½ï½ It
This relation is known as Joules law of heating.
Power, P = 12 W
Potential difference, V =12 V
Time duration of current flow, t = 1 min = 60 s
H = P ï½ï½ï½ï½ t
= 12 W ï½ï½ï½ï½ 60 s
= 720 J
The heat generated by the instrument of 12 W in a minute is 720 J.
The given figure shows a circuit consisting of three resistors R1, R2and R3connected in parallel. The total current in the circuit (I) gets divided among the three resistors as I1, I2and I3.
I = I1+ I2+ I3
Applying Ohms law to each resistor,
Let the equivalent resistance of the circuit be Req.
Applying Ohms law to the equivalent circuit,
An ammeter has to be connected in series with the combination of all three resistors so that the current passes through the ammeter becomes equal to the total current through the circuit.
The voltmeter has to be connected in parallel to that resistor across which the potential difference has to be measured.
Question 18 ( 5.0 marks)
Write the names and symbols of two most reactive metals belonging to group 1 of the periodic table. Explain by drawing electronic structure how either one of the two metals reacts with a halogen. With which name is the bond formed between these elements known and what is the class of the compound so formed known? State any four physical properties of such compounds.
What is meant by refining of metals? Name the most widely used method of refining impure metals produced by various reduction processes. Describe with the help of a labelled diagram how this method may be used for refining of copper.
Two most reactive elements of group 1 of the periodic table are sodium (Na) and potassium (K)
As the ions of sodium and chlorine are oppositely charged, they attract each other by strong electrostatic forces. The reaction between sodium and chlorine can be represented as follows:
The bond formed between these elements is known as ionic or electrostatic bond.
Sodium chloride belongs to the class ionic compounds.
Following are the four physical properties of ionic compounds.
1. Ionic compounds exist in solid state
2. Ionic compounds have high melting and boiling points
3. Ionic compounds are soluble in polar solvents such as water and insoluble in non-polar or organic solvents (kerosene and petrol).
4. Ionic compounds conduct electricity in their molten or aqueous state.
Refining is the process of obtaining pure metal from its impure sample.
Electrolytic refining is the most widely used method of refining impure metals produced by various reduction processes.
Electrolytic refining of copper
In this process, anode is made of a large block of impure metal and cathode is made of a thin strip of pure metal. The electrolyte used in the process is acidified copper sulphate solution.
When electric current is passed through the electrolyte, the positively charged metal ions present in the electrolyte get attracted towards the negatively charged cathode. When metal ions reach near the cathode, they gain electrons from it and get deposited there. Hence, as the time increases, the cathode becomes thicker and thicker.
As the metal ions from the electrolyte move towards the cathode, an equal amount of ions are released by the anode into the solution. Therefore, as the time increases, the size of the block of impure metal keeps on decreasing i.e. anode becomes thinner and thinner.
The soluble impurities present in the impure metal block go into the electrolytic solution. And the insoluble impurities settle down at the bottom of the container below the anode and are known as anode mud.
Question 19 ( 1.0 marks)
Name the hormone that helps in regulating level of sugar in our blood. Name the gland that secrets it.
Insulin helps in regulating sugar level in our blood. This hormone is secreted by pancreas gland.
Question 20 ( 1.0 marks)
A person lives near a forest. Make a list of four items which he can get from the forest to meet his daily needs.
Four products that a person will get from the forest are timber, firewood, honey and animal meat.
Question 21 ( 1.0 marks)
Name the green dot like structures in some cells observed by a student when a leaf peel was viewed under a microscope. What is this green colour due to?
The green dot-like structures in some cells observed by the student when a leaf peel was viewed under a microscope are chloroplasts. The green colour is due to the presence of green pigment chlorophyll.
Question 22 ( 2.0 marks)
What is phototropism? Describe an activity to demonstrate phototropism.
The growth movement in plants in response to light stimulus is known as phototropism.
To demonstrate phototropism in plants a sunflower plant is taken and kept in sunlight. It will be observed that the flower head of sunflower will move from east to west along with the movement of Sun. This shows that the flower head of sunflower is positively phototropic and moves in response to sunlight stimulus.
Question 23 ( 2.0 marks)
List any two differences between pollination and fertilisation.
Pollination is the transfer of pollen grains carrying male gametes from the anther to pistil of a flower. Pollination is of two types—self pollination and cross pollination.
Fertilization is the fusion of male and female gamete to form a zygote. It is also of two types—internal fertilization and external fertilization.
Pollination occurs with the help of certain agents such as wind, water or animals
Fertilization occurs after pollination when the pollen grain resides on stigma and forms a pollen tube to transfer the male gamete into the embryo sac in the ovary.
Question 24 ( 2.0 marks)
Give one example each of characters that are inherited and the ones that are acquired in humans. Mention the difference between the inherited and the acquired characters.
Eye colour or hair colour of a person is an example of inherited character whereas body weight is an example of acquired character.
The basic difference between inherited and acquired character is that inherited character is passed on from parent to offspring. On the other hand, acquired characters are acquired by an individual during his lifetime depending upon his lifestyle.
Question 25 ( 3.0 marks)
How is ozone formed in the higher level of atmosphere? Damage to the ozone layer is a cause of concern. Justify this statement.
The ozone layer is continuously formed in the atmosphere because of the action of UV rays on molecular oxygen. The high-energy UV radiations break down O2molecules present in upper layers of the atmosphere into nascent oxygen.
Then, this free oxygen atom combines with an oxygen molecule to form ozone.
Damage to the ozone is a cause of concern; this is because ozone depletion has created an hole in the ozone layer over the Arctic region.
Damage in the ozone layer allows the harmful UV rays to reach the earth surface. UV rays can cause—
ï½ï½ï½ï½ skin cancer, ageing and corneal cataracts in human beings.
ï½ï½ï½ï½ death of many phytoplankton leading to the increase in the rate of global warming. Increase in the global warming rate, in turn, leads to the melting of Arctic ice cap. This may further result in the increase in the sea level.
Thus, it is justified to say that damage to the ozone is a cause of concern.
Question 26 ( 3.0 marks)
Write the full form of DNA. Name the part of the cell where it is located? Explain its role in the process of reproduction of the cell.
The full form of DNA is Deoxyribonucleic acid.
It is the genetic material found in the chromosomes, which are present in the nucleus of a cell.
It is a chemical that carries genetic information required by the cells to divide and produce proteins.
DNA plays an important role in the reproduction of a cell. The reproducing cell produces an identical copy of DNA through some cellular mechanism. Since the newly formed copy of DNA lacks an organised cellular structure, the cell gets divided to provide cell cover to the newly formed DNA. Thus, two daughter cells are formed from the single cell as a result of the copying of DNA.
Question 27 ( 5.0 marks)
Explain the process of digestion of food in mouth, stomach and small intestine in human body.
(a) List the three events that occur during the process of photosynthesis. Explain the role of stomata in this process.
(b) Describe an experiment to show that sunlight is essential for photosynthesis.
The process of digestion of food in mouth, stomach and small intestine is described as follows:
Mouth—Digestion of food begins in the mouth. Saliva present in mouth contains a digestive enzyme, called salivary amylase, which breaks down starch into sugar.
Stomach—Stomach stores and mixes the food received from the oesophagus with gastric juices. The main components of gastric juice are hydrochloric acid, mucus and pepsinogen.
Hydrochloric acid dissolves bits of food and creates an acidic medium. In this medium, pepsinogen is converted to pepsin, which is a protein-digesting enzyme. Mucus protects the inner lining of the stomach from the action of HCl.
Small intestine—Small intestine is the site for complete digestion of carbohydrates, proteins and fats.
Small intestine produces intestinal juice from the glands present in its wall. The intestinal juice helps in further digestion of food. Small intestine also obtains digestive juices from liver and pancreasthat helps in mixing of food.
The liverproduces bile juice that causes emulsification of fats and the pancreas produces pancreatic juice for digesting proteins and emulsified fats.
This digested food is finally absorbed through the intestinal walls.
a. The events that occur in plants during photosynthesis are—
ï½ï½ï½ï½ Absorption of sunlight by the green pigment chlorophyll
ï½ï½ï½ï½ Conversion of light energy into chemical energy and the splitting of water molecule into oxygen and hydrogen
ï½ï½ï½ï½ Reduction of carbon dioxide into glucose
Role of stomata
Stomata are tiny pores present mainly on the surfaces of leaves. They are also present on the surface of young stems and roots. Stomata are mainly engaged in the exchange of gases (entry of CO2and release of O2) associated with photosynthesis.
b. Sunlight is essential for photosynthesis
Place a healthy, green, potted plant in a dark room for 12 days. This is done to ensure that the plant consumes all its reserve food and the leaves do not contain any starch. Then, cover a portion on both sides of a green leaf with two uniform pieces of black paper. Fix the cover in position with two paper clips.
Now, expose this plant to bright light. After a few hours, remove the leaf and decolourise it with alcohol. Now, test the presence of food (starch) by putting iodine solution on the leaf.
It can be observed that the covered portion of the leaf does not show any presence of starch (food).
This is because plants store the food prepared by through the process of photosynthesis as starch. Starch reacts with iodine solution to give blueblack colour.
In the performed experiment, only those portions of the leaf that were exposed to sunlight could photosynthesise. Hence, the uncovered portion of the leaf gives blueblack colour when tested with iodine.
The covered portion of the leaf did not receive any sunlight. Hence, starch was not produced in this portion. So, it does not change its colour when treated with iodine solution.
Thus, it can be concluded that the sunlight is essential for photosynthesis.