(c) An atom has electronic configuration 2,8,7. To which of the following elements would it be chemically similar ?
(i) N (7) (ii) F (9) (iii) P (17) (iv) Ar (18)
Answer: (ii) F (9)
(d) Anaerobic respiration takes place in:
(i) Mitochondria (ii) Chloroplasts (iii) Nucleus (iv) Cytoplasm
Answer: (iv) Cytoplasm
(e) Which of the following diseases is caused due to insufficient secretion of thyroxin hormone ?
(i) Beriberi (ii) Goiter (iii) Diabetes (iv) Dwarfism
Answer: (ii) Goiter
(f) If a cross is made between the plants having tall (TT) and dwarf (tt) genetic composition, which type of plants we will obtain in the next generation ?
(i) Tall (TT) and dwarf (tt) both (ii) Only tall
(iii) Only dwarf (iv) None of the above
Answer: (ii) Only tall
(g) Which of the following lenses would you prefer to use while reading very small letters ?
(i) A convex lens of focal length 50 cm (ii) A convex lens of focal length 5 cm
(iii) A concave lens of focal length 50 cm (iv) A concave lens of focal length 5 cm
Answer: (ii) A convex lens of focal length 5 cm.
(h) The change of focal length of an eye-lens is caused by the action of the-----
(i) Pupil (ii) Retina (iii) Ciliary muscles (iv) Iris
Answer: (iii) Ciliary muscles
(i) Which of the following terms does not represent electrical power in a circuit ?
(i) IR2 (ii) I2R (iii) V2/R (iv) VI
Answer: (i) IR2
(j) Which of the following constitute a food chain ?
(i) Grass, fish and goat (ii) Goat, cow and elephant
(iii) Grass, goat and human (iv) Grass, wheat and mango
Answer: (iii) Grass, goat and human
Section-B
2. Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide). Write the chemical equation of this reaction and mention the type of this chemical reaction. 1
Answer: CaO(s) + H2O(l) → Ca(OH)2(aq)
The reaction is a combination reaction.
3. Define allotrope of an element with examples. 1
Answer: An element can exist in more than one form in the nature, this property of an element is called allotropy and different forms of the element are called its allotrope. For example, allotrope of carbon - diamond and graphite.
4. What is catenation ? 1
Answer: Carbon can form a large number of molecules by forming bonds between itself. This property of carbon is called catenation.
5. Why are traits acquired during the life time of an individual not inherited ? 1
Answer: The traits acquired by an organism during its lifetime are not passed on to its offspring because these traits are not stored in the DNA of the organism and therefore cannot make change in the DNA of the germ cell.
6. Why do stars twinkle ? 1
Answer: The direction of light rays coming from a star is constantly changing due to atmospheric refraction. Therefore, the apparent position of the star changes and the star twinkles.
7. Translate the following statements into chemical equations and then balance them. 1 + 1 = 2
(i) Hydrogen sulfide gas burns in air to give water and sulfur dioxide
Answer: 2H2S(g) + 3O2(g)→ 2H2O(l) + 2SO2(g)
(ii) Potassium metal reacts with water to produce potassium hydroxide and hydrogen gas.
Answer: 2K(s) + 2H2O(l) → 2KOH(aq) + H2(g)
8. You have two solutions A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration ? Which of these is acidic and which one is basic? 1 + 1 = 2
Answer: Solution A has more hydrogen ion concentration. A is acidic, B is basic.
9. Name the green dots contained by the leaves. What function do they perform? 1 + 1 = 2
Answer: The name of the green dots on the leaf is chloroplast. The green pigment chlorophyll present in chloroplast helps the plant in the process of preparation of food through photosynthesis.
10. How does muscle cells change their shape? 2
Answer: Muscle cells contain certain special types of proteins. These proteins can change shape and arrangement when stimulated by electrical impulses causing the muscle cells contract. As a result, the shape of the muscle cells changes.
OR
What is the importance of iodine in our body? 2
Answer: Our body needs iodine for the release of thyroxine hormone by the thyroid gland. The hormone thyroxine regulates the metabolism of carbohydrates, proteins and fats in our body. Iodine deficiency can also lead to goiter diseases.
11. How reproduction through spores is beneficial for an organism? 2
Answer: Reproduction by spores can be beneficial for an organism because:
(1) The spores are covered by a sufficiently thick covering, so they can survive for many days even in adverse environments.
(2) Spores can produce innumerable plants in a very short period of time.
OR
How does spirogyra reproduce? 2
Answer: Spyrogyra reproduces through the process of fragmentation. Upon maturation, it splits into a few small fragments and a new generation is formed from these small fragments.
12. Draw a ray-diagram when an object is placed at twice of the focal length of a convex lens. 2
OR
Define power of a lens. What is its SI unit? 1 + 1 = 2
Answer: The ability of a lens to converge or diverge light rays is called the power of a lens. Its SI unit is diopter.
13. A current of 0.6 A is drawn by a filament of an electric bulb for 5 minutes. Find the amount of electric charge that flows through the circuit. 2
Answer: Given, electric current (I) = 0.6 A
Time (t) = 5 minutes = 5 * 60 seconds = 300 seconds
We know that Q = It
= 0.6 * 300 coulombs
= 180 coulombs
OR
How electric charges flow inside a wire. Explain. 2
Answer: When a potential difference is applied to both sides of the conductor, an electric charge flows through the conductor. Potential difference forces the free electrons in the conductor to move in a particular direction through the conductor.
14. How can you help in reducing the problem of waste disposal ? 2
Answer: The following steps can be taken to reduce the problem of waste.
(i) Biodegradable wastes can be used to make compost.
(ii) The amount of waste can be reduced by reducing the use of non-biodegradable materials.
(iii) Recycling of plastic, paper, glass and metallic objects can be used to make other useful materials.
(iv) Some waste items like used up bottles of jams, jellies, pickles etc. can be reused to keep various items in the kitchen.
15. State two problems caused by non-biodegradable wastes what we generate. 2
Answer: The two problems caused by non-biodegradable wastes that we have created are-
1) Pollution of soil, water and air.
2) Negative effect on the ecosystem.
3) Biological magnification etc.
16. What is the role of split ring in electric motor? 2
Answer: In electric motor, the split ring acts as a commutator. It reverses the direction of the current in the two arms of the coil which reverses the force acting on the two arms, so that, coil rotates in the same direction continuously.
17. Take a small amount of copper oxide in a beaker. Gradually add dilute hydrochloric acid while stirring and answer the following questions. 1 + 1 + 1 = 3
(i) What is the color of the solution ?
Answer: The color of the solution is blue-green
(ii) What has happened to copper oxide?
Answer: Copper oxide has dissolved in the solution.
(iii) Write the balanced chemical equation for the above reaction.
Answer: CuO(s) + 2HCl(l)→ CuCl2(aq) + H2O(l)
OR
What is brine ? What is the product formed when electricity is passed through this brine? Write the balanced chemical equation for the above reaction. 1 + 1 + 1 = 3
Answer: The aqueous solution of sodium chloride (NaCl) is called brine. When electricity flows through the brine, it produces sodium hydroxide (NaOH). The balanced chemical equation for the reaction is
2NaCl(aq) + 2H2O(l) → 2NaOH(aq) + Cl2(g) + H2(g)
18. (a) A solution of a substance X is used for white washing. 1 + 1 = 2
(i) Name the substance X and write its formula.
(ii) Write the reaction of the substance X named in (i) above with water.
Answer: (i) The name of the substance X is Calcium Oxide and the symbol is CaO
(ii) The reaction of X with water is
CaO(s) + H2O(l) → Ca(OH)2(aq)
(b) Identify the substance that is oxidized and the substance that is reduced in the following reaction.
CuO(s) + H2(g)→ Cu(s)+ H2O(l)
Answer: CuO ----- is reduced
H2 ----- is oxidised
OR
(a) A shiny brown coloured element 'X' turns black when heated in air. Write the name of element X and the resulting black colour compound.
(b) Why do we apply paint on iron articles ? 1 + 1 + 1 = 3
Answer: (a) The element X is copper (Cu) and the resulting black coloured compound is copper oxide (CuO).
(b) We apply paint on iron articles to prevent them from corrosion.
19. State modern periodic law. How could the modern periodic table remove various anomalies of Mendeleev's periodic table ? 1 + 2 = 3
Answer: The modern periodic law states that ----- "Properties of elements are the periodic function of their atomic numbers."
The modern periodic table was prepared on the basis of atomic number of the elements which removes various anomalies of Mendeleev's periodic table as follows:
(1) Mendeleev's periodic table could not give a correct place to hydrogen. But the modern periodic table eliminates this problem and gives hydrogen a definite place. The atomic number of Hydrogen is 1, so the position of hydrogen become clear in the periodic table.
(2) The isotopes of the elements were discovered after Mendeleev's classification and created a challenge to Mendeleev's periodic table. But the modern periodic table eliminates this problem and gives isotopes the same place.
(3) Atomic number of an element is unique. So the controversy regarding position of an element comes to an end.
OR
What is Newland's Law of Octaves ? What were the limitations of Newlands' Law of octave ? 1 + 2 = 3
Answer: Newlands attempted to arrange the elements in order of their atomic masses. He found that every eighth element has properties similar to that of first, which is known as Newlands' law of octaves.
The limitations of Newlands' law of octave are ---
(1) The law is applicable only up to calcium.
(2) Newlands assumed that there are only 56 elements in nature and assumed that no more elements will be discovered in the future.
(3) Newlands, in his list not only arranged the two elements in the same place, but also included some elements which have different properties, in the same column.
20. What is pollination? What is the difference between pollination and fertilization? How does self-pollination differ from cross-pollination? 1 + 1 + 1 = 3
Answer: In the sexual reproduction of flowering plants, the phenomenon of transference of pollen grains from the stamen to the stigma is called pollination.
There is a difference between pollination and fertilization. Pollination is an external process, fertilization is an internal process. Pollination results in the formation of pollen tube, fertilization results in formation of gamete.
In self-pollination, the pollen grains are transferred from the stamens to the stigma of the same flower, whereas in the cross pollination, the transfer of pollen takes place from one to another flower by agents.
OR
How does menstruation cycle occur? 3
Answer: One egg is released from the ovary of an women every month. The uterus prepares itself to receive a fertilized egg by thickening the inner lining. If the egg released by the ovary is not fertilized, the lining of the uterus breaks down and comes out through the vagina along with unfertilized eggs and mucus. This process repeats itself every month. The female hormones also play an important role in this process.
21. What factors could lead to the rise of a new species ? Explain 1 + 2 = 3
Answer: The following factors lead to the rise of a new species ---
(1) Variation caused by natural selection: Variations created in a species gives an organism a chance to survive and help in the emergence of a new species.
(2) Genetic drift: Changes in the genetic makeup contribute to the emergence of new species.
(3) Geographical isolation: Nationalization will take place only when there is geographical segregation along with diversity.
OR
What do you understand by geographical isolation? Will this be a major factor in the speciation of a self-pollinating plant species? Why or why not? 1 + 2 = 3
Answer: When a population of the same species has to be separated for a long period of time due to different geographical constraints like mountains, rivers, etc., it is called geographical isolation.
Geographical isolation may not be a major cause of speciation for self-pollinated plant species as self-pollinated plants do not depend on other plants for pollination and fertilization. Since self-pollination occurs within the same plant, geographical isolation cannot be a major cause of speciation in such plants.
22. Name the parts of the human brain. State the activities that are controlled by the cerebellum. 1 + 2 = 3
Answer: The different parts of the human brain are --- the fore brain --- cerebrum,
the mid brain ---- Hypothalamus and
the hind brain- Pons,cerebellum, medulla
Activities controlled by the cerebellum are -----
(1) Various voluntary activities.
(2) Maintaining body posture and balance.
OR
What is auxin? How does it aid in the growth of a plant ? 1 + 2 = 3
Answer: Auxin is a plant hormone that helps cells grow larger and taller.
When light is available from only one side of the plant, the auxin flows to the part of the stem which is not exposed to sunlight. The concentration of auxin in the part of the non-illuminated stem stimulates the elongation of the cells in it. As a result, the stem of the plant moves towards the light.
23. What do you mean by Dispersion of white light? Draw the ray diagram to show the dispersion of white light when passes through a prism. 1 + 2 = 3
Answer: White light is a composition of seven colors. In white light, although its components are not seen separately, but one color is distinct from the other. The separation of these components of white light into its constituent colors is called dispersion of light.
26. Can any sources of energy be pollution free? Why or why not? Write down the two limitations of energy that can be obtained from the ocean. 1 + 2 = 3
Answer: A source of energy can never be completely pollution free. This is because when the source is prepared or used, it affects the environment in one way or another.
There are two major limitations to the power that can be obtained from the ocean
(1) Such projects are applicable only in areas where the sea tide is very high. As soon as the tide recedes, production stops.
(2) This is possible only in coastal areas.
27. (a) Names two metallic oxides which dissolved in water. 1
Answer: Metallic oxides that dissolved in water - sodium oxide (Na2O), calcium oxide (CaO).
(b) What chemical process is used for obtaining a metals from its oxides? Explain with example. 2
Answer: Reduction method is used to obtain metals from its oxides. Metal oxides are reduced to the corresponding metal by using suitable reducing agent such as carbon. For example, when zinc oxide is heated with carbon, the metal reduces to zinc. This method is called carbon reduction method.
ZnO (s) + C (s) ー> Zn (s) + CO (g)
(c) You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels. 2
Answer: If a copper vessel is exposed to air for a long time, a green colored coating of copper carbonate forms on the vessel. Lemon juice contains citric acid and tamarind juice contains tartaric acid. These acids dissolves the green color coating of copper carbonate and cleans the vessel.
OR
(a) Identify the most reactive and least reactive metals among the following.
Al, K, Cu, Au. 1
Answer: The most reactive metal is K, the least reactive metal is Au.
(b) Define the following terms with the example. 2
(i) Minerals
(ii) Ore
Answer: (i) Minerals- The elements or compound which occur naturally in the earth's crust are called minerals. Eg. calcium carbonate.
(ii) Ore- A mineral which contains a very high percentage of a particular metal and the metal can be extracted profitably from it is called an ore of the metal. For example, Cinnabar (HgS) is an ore of mercury.
(c) Explain the electrolytic refining used for refining of metals. 2
Answer: Metals obtained from ores in various ways are not pure. They have some impurities with them. Pure metal can be obtained by removing these impurities. The most widely used method of refining metals is the electrolytic refining method.
Metals like copper, zinc, tin, nickel etc. are refined using this method. In this method a sheet of impure metal is used as anode and a sheet of pure metal is used as cathode. A solution of the salt of the metal is taken as electrolyte. Pure metal is dissolved in the solution from the sheet of impure metal used as anode, when an electric current is passed through the electrolyte. The same amount of pure metal goes from the electrolyte to the cathode. This process is repeated until whole of the pure metal in anode goes into the solution. This is how we get pure metal in the cathode.
28. (a) Draw the structures of the isomers for butane (C4H10). 1
Answer: Structure of isomers of butane are
(b) What is substitution reaction? Explain with example. 2
Answer: Chlorine, Bromine, OH etc can replace the hydrogen atoms of a saturated hydrocarbon one by one. This types of reactions are called substitution reaction.
Example: CH4 + Cl2—―——→ CH3Cl + HCl (in presence of sunlight)
(c) How would you distinguish experimentally between an alcohol and carboxylic acid? 2
Answer: The difference between alcohols and carboxylic acids can be shown as follows.
(1) With the help of blue litmus paper: Carboxylic acids can change the color of blue litmus paper to red but alcohol cannot.
(2) With the help of Sodium Hydrogen Carbonate (NaHCO3): Sodium Hydrogen Carbonate will react with carboxylic acid with the evolution of a gas, but the alcohol does not react in any way.
OR
(a) Draw the structures of the isomers for bromobutane. 1
Answer: Structures of isomers of bromobutane are
(b) How does ethanoic acid react with carbonates and hydrogen carbonates? Write the chemical reactions. 2
Answer: Ethanoic acid reacts with carbonates and hydrogen carbonates to form sodium ethanoate and carbon di oxide gas. Reactions are as shown below:
2CH3COOH + Na2CO3 → 2CH3COONa + H2O +CO2
CH3COOH + NaHCO3→ CH3COONa + H2O +CO2
(c) Explain the mechanism of the cleaning action of soap. 2
Answer: Most dirt particles have oily properties and we know that oil is insoluble in water. The molecules of soap are the sodium or potassium salts of long-chain carboxylic acids. The ionic poles of soap are soluble in water, while the carbon chain is soluble in oil. Thus the molecules of soap form aggregates in water called micelles, which is called froth in common language.
Here the non-polar poles of the molecules are on the oil side and the polar poles are on the outer side. This is how soap froth helps to dissolve the dirt particles in water.
29. What are 'Biological catalysts'? Name two such catalysts. Discuss the role they play in our body. What is the function of hydrochloric acid released by the gastric glands into the stomach? 1 + 1/2 + 1/2 + 2 + 1 = 5
Answer: Biological catalysts are substances that can break down complex molecules of food into simpler substances. Examples of bio-catalysts are pepsin, trypsin, amylase, etc.
The food we eat is very complex in nature. It is very important that the food is transformed into the smallest form inside our stomach. In order to digest this complex type of food in the digestive tract, it is necessary to change the complex food to a simple state. In our body, this process is done by biological catalysts. These organic molecules break down complex molecules of carbohydrates, proteins, fats, etc. into simpler molecules so that they can be easily absorbed in the blood of our body.
The main function of hydrochloric acid, which is secreted into the stomach by the gastric glands are: hydrochloric acid acidify the food in the stomach so that the action of pepsin is intensified. It also destroys the germs present in the food.
OR
How is food transported in plants? What are the differences between the transport of materials in xylem and phloem? 2+3=5
Answer: We all know that plants produce food through the process of photosynthesis. It is very important that the food produced in the leaf through the process of photosynthesis flows from that place to other parts of the plant body. The transport of soluble substances produced in the process of photosynthesis is called translocation of food. The circulation of food in the body of the plant is done through the circulatory network called phloem. In addition to the substances produced in the process of photosynthesis, phloem also carries amino acids and some other substances. These substances are transported upwards and downwards, especially to the stalks, fruits, seeds and the developing organs, with the help of the sieve tubes and the companion cells attached to the phloem.
The process of translocation of food through phloem is always associated with some energy. Transportation of substances such as sucrose use energy extracted from ATP as they move into the phloem tissue. This increases the osmotic pressure inside the phloem, causing water to move inside it. This pressure causes the material to move to the low pressure phloem. This allows the plant to transmit the substance or food to the needy areas of the plant body.
The differences in the transportation of xylem and phloem are:
(1) The xylem carries water and mineral salts in the plant body, the phloem carries the food prepared in the leaves to various organs.
(2) The transport of xylem is in upward direction, the transport of phloem is in both upward and downward direction.
(3) The circulation through the xylem tissue occurs with the help of simple physical forces. Transportation through phloem always uses stored energy.
30. An object of size 70 mm is placed at a distance of 27 cm in front of a concave mirror of focal length 18 cm. At what distance from the mirror should a screen be placed, so that a sharp focussed image can be obtained. Find the size and nature of the image. 5
Answer: Given
u= -27 cm
f= -18 cm
h= 70 mm=7 cm
v=?
h'= ?
We know that,
1/v + 1/u = 1/f
1/v = 1/f-1/u
1/v = (1/-18) - (1/-27)
1/v = -3+2/54
v = -54
Therefore, the screen should be placed at a distance of 54 cm from the mirror so that a focussed image can be obtained.
Again, h'/h = -v/u
h'/7 = -(-54/-27)
h' = -14
Therefore size of the image is 14 cm and its nature is real.
OR
A concave lens has focal length of 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens? Also find the magnification produced by the lens. what is the nature of the image? 5
Answer: Given, f = -15 cm
v = -10 cm
u =? /
m =?
We know that,
1 / v-1 / u = 1 / f
1 / u = 1 / v-1 / f
1 / u = 1 / -10 -1 / -15
1 / u = -1/30
u = -30
The object should be placed at a distance of 30 cm from the lens
Again,
Magnification, m = v / u = -10 / -30 = 1/3
Therefore, the image is virtual and smaller in size than the object
31. Give two examples of fossil fuel. How can you as an individual contribute to the management of: 1+2+2=5
(a) Forest and Wildlife
(b) Water Resources
Answer: Two examples of fossil fuels are coal and petroleum.
(a) For Forest and Wildlife management
(1) Efforts should be made to prevent environmental pollution that harm forests and wildlife.
(2) Awareness should be created among the people about the importance of forest and wildlife conservation.
(3) Cutting of trees and poaching of wild animals should be strictly prohibited.
(b) For management of water resources
(1) Conservation of water resources through limited use.
(2) Protection of water resources from pollution.
(3) Practicing water harvesting through different methods.
OR
What do you mean by water harvesting? Compare the traditional systems of water harvesting between hilly areas and plains.
Answer: Biomass production can be increased by conserving soil and water through watershed management. The goal is to develop primary resources such as soil and water. The development of this soil and water increases the production of secondary resources such as plants and animals. Water harvesting is a very old practice in India.
There are considerable differences between traditional water harvesting methods in hilly areas and plains. In hilly areas, people either store water in ponds, lakes, etc., or conserve water in a variety of ways, either through soil or by embankment. On the other hand, water is stored in the plains by building river dams or by managing to store water in the tanks build in the terrace.
For solved question paper of HSLC, 2020 in Assamese medium please visit the link: https://bigyanbharati.blogspot.com/2020/07/solved-question-paper-of-hslc-2020.html
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